Fitzsimons Army Hospital, also known as Fitzsimons General Hospital, renamed Fitzsimons Army Medical Center in 1974, and Fitzsimons Building in 2018 was a U.S. Army facility located on 577 acres (234 ha) in Aurora, Colorado. The facility opened in 1918 and closed in 1996. The grounds were then redeveloped for civilian use as the Anschutz Medical Campus and the Fitzsimons Innovation Community.

The land the facility occupies is the sacred and ancestral territory of the Pawnee and Jicarilla Apache peoples. These groups controlled the land in the 1500s.

The facility was founded by the United States Army during World War I arising from the need to treat the large number of casualties from chemical weapons in Europe. Denver's reputation as a prime location for the treatment of tuberculosis led local citizens to lobby the Army on behalf of Denver as the site for the new hospital. In February 1918, the War Department recommended to Congress $500,00 be expended on constructions of the Denver hospital. Additionally, local business owners raised $150,000 to purchase the property east of Denver that previously belonged to A. H. Gutheil Nursery. U.S. Army General Hospital No. 21, as it was first called, had ground breaking in April 1918, was formally dedicated and opened on October 13, 1918, in Aurora, which at the time had a population of less than 1,000. The campus consisted of 86 stucco buildings and capacity for 1,400 patients. The first commander of the hospital was Colonel William P. Harlow, a Boulder native. He began his term on August 27, 1918, and had been the Dean of the University of Colorado Medical School before World War I. Elizabeth D. Reid served as the first head nurse. Construction of the hospital was not officially completed until 1919. The final construction cost was $3.2 million. The Camp Speer, Colorado, post office operated from December 5, 1918, until February 14, 1919.

On July 1, 1920, the facility was formally renamed the Fitzsimons General Hospital after Lt. William T. Fitzsimons, the first American medical officer (a surgeon) killed in World War I. By the 1920s, the hospital was the largest tuberculosis hospital in the United States using heliotherapy as one of the major forms of treatment. The hospital admitted and discharged approximately 300 patients per month while also serving as a general hospital for active military and veterans in the Denver area. In 1926 the Fitzsimons radio station KEUP was started.

The facility was being prepared for closure by the Army during the economic depression of the 1930s. In April 1933, Surgeon General R. U. Patterson sent a radiogram stating that Fitzsimons would be abandoned and all patients transferred. However, Denver's reputation for treating tuberculosis and the consequences of losing 1,000 jobs at Fitzsimons led to citizen lobbying for Denver to be the site of a new Army hospital. U.S. Senator Lawrence C. Phipps was also a promotor of Fitzsimons Army Hospital and his efforts led to Congress approving funding in November 1934 to keep the hospital open. The Army maintained the hospital in the budget for a few years before asking for work-relief funds to rebuild and modernize the facility in 1935. From 1935-1936 several improvement projects were carried out by the Works Progress Administration (WPA). President Franklin D. Roosevelt visited Fitzsimons on October 12, 1936, and vowed to maintain the hospital. In 1937, the land needed for construction of a new facility was officially turned over to the federal government, which paved the way for future development. In 1938, Congress approved $3.75 million in Public Works Administration funds for a new hospital and construction of a new main building, known as Building 500, began in January 1939 and was completed in 1941. At the time, it was the largest structure in Colorado and the largest single hospital structure ever built by the Army. The building completed with 290,000 sq ft, 1,800 rooms, ten stories, and 2,252 beds. The property was divided into two sections along a line extending through Monteview Street. Property north of the line was designated for commercial development. Property to the south was designated for medical and educational purposes, which is the current day School of Medicine and many hospitals. Building 500 got its name from its location exactly at the center of the south property and 500 yards from Montview Street. The building construction followed a Modernistic style, which was state-of-the-art for military hospitals at the time. The supervising architect for the Army Quartermaster Corps, L. M. Leisenring oversaw the design and construction of the building in a Modernistic Art Deco style. Building materials included several blended colors of face brick, Texas sandstone, Yule Marble for the main entrance, Colorado Travertine stone for the walls, and granite for the paving and curbs under the entrance. The grand portico above the main entrance was inscribed with three Latin phrases: Vita Brevis Ars Vero Longa, meaning "Life is short, art is enduring", Salus Virtus et Robur Artubus Scientia et Virtute et Bonis Artibus, meaning "Health, strength and vigor to the sinews (body) with the help of science, virtue and the arts", and Non Sibi Sed Proximo ,"Not for himself but for the next one to him". At the time the building was dedicated by Congressman Lewis on December 3, 1941, it had 290,000 sq ft and 608 beds.

Four days after the dedication, Pearl Harbor was attacked and soldiers, sailors, airmen, and Marines who injured began arriving on December 17. At the peak of its development during World War II, the number of hospital beds increased to 3,500 and the hospital contained as many as 5,000 patients at a time. This was accomplished by the hasty construction of many temporary buildings. The hospital campus had also grown to become the largest military hospital in the world with 322 buildings on about 600 acres. In April 1943, a post newspaper "The Stethoscope" was first published and formal publication lasted until the closure of the base. In 1944, the first members of the Women's Army Corps (WAC) arrived at Fitzsimons. In 1947, the Prisoner of War camp was razed. In 1948, Fitzsimons became one of the first hospitals to use streptomycin to treat tuberculosis.

In the 1950s, tuberculosis cases dropped with improvements in public health and lung cancer and other chest diseases became the focus. The hospital was renamed Fitzsimons Army Hospital in July 1950 and a pre-school and kindergarten were opened. In 1952, the 8th floor auditorium was named for Col. George E. Bushnell, who was responsible for inspecting and identifying the site of the future hospital in 1918. In 1953, Korean prisoners of was were treated at Fitzsimons and three departments were established: Medicine, Surgery, and Neuropsychiatry. In 1955, a new chapel and credit union were opened.

The facility was used heavily during World War II to treat returning casualties and became one of the Army's premier medical training centers. In the 1950s, Dwight Eisenhower received treatment at the facility three separate times for his heart condition while he was president. In the early morning hours of September 24, 1955, about five weeks into a "work and play" vacation at his in-laws' house in Denver, he suffered a myocardial infarction and was placed in an oxygen tent at the facility. He spent seven weeks convalescing in his suite on the eighth floor (Room 8002) of Building 500.