"Sick man of Europe" is a label given to a state located in Europe that is experiencing economic difficulties, social unrest or impoverishment. It is most famously used to refer to the Ottoman Empire (predecessor of present-day Turkey) whilst it was in a state of decline in the 19th century.

Emperor Nicholas I of the Russian Empire is considered to be the first to use the term "Sick Man" to describe the Ottoman Empire in the mid-19th century. The characterization existed during the "Eastern question" in diplomatic history, which also referred to the decline of the Ottoman Empire in terms of the balance of power in Europe. After the dissolution of the Ottoman Empire in the early 20th century, the term has been applied to other states. In modern usage, the term has faced criticism due to its origins and arguable over-usage.

Throughout the 1960s to the 1980s, the term was also most notably used for the United Kingdom when it lost its superpower status as the Empire crumbled and its home islands experienced significant deindustrialization, coupled with high inflation and industrial unrest – such as the Winter of Discontent – including having to seek loans from the International Monetary Fund (IMF). Since the mid-2010s and into the 2020s, the term being used for Britain began to see a resurgence after Brexit, a cost-of-living crisis and industrial disputes and strikes becoming more commonplace.

As of 2024, Germany is most commonly referred to as the "Sick Man of Europe" due to its consistently stagnant economy, and in particular its industrial base, since the COVID-19 pandemic, as well as the reduction in imports of inexpensive natural gas from Russia after the Russian invasion of Ukraine. This has been demonstrated by Germany having the lowest GDP growth amongst the large G7 industrialised economies compared to the pre-pandemic level. The country had previously been referred to as the "Sick Man" during the late 1990s to early 2000s.

In 2025, BBC InDepth Paris correspondent Hugh Schofield wrote that France was at risk at becoming the new Sick Man of Europe.

Russian Tsar Nicholas I (r. 1825–1855), seeking to expand into parts of the Ottoman Empire during the Eastern Question, had described Turkey as "sick" or "sick man" during his meeting with Austrian chancellor Metternich (in office 1809–1848) in Münchengrätz, two months after the Treaty of Hünkâr İskelesi in September 1833. In his own writing, Metternich said he had argued against this characterization. Conventionally, foreign minister Metternich was opposed to the characterization of the Ottoman Empire as "sick man of the Bosphorus" because this could lead to his country, the Austrian Empire, becoming the "sick man of the Danube". Other historians, evaluating the conservative "Holy Alliance" of the time, have seen Metternich's foreign policy as aligned with Nicholas, including the policy towards the Ottoman Empire.

British statesman John Russell in 1853, in the run-up to the Crimean War, reported that Nicholas I of Russia described the Ottoman Empire as "a sick man—a very sick man", a "man who has fallen into a state of decrepitude", and a "sick man ... gravely ill".

There has been some degree of debate about the source of the quotation, which often relies on historical documents held or communicated personally. Historian Harold Temperley (1879–1939) gave the date for the first conversation as 9 January 1853, like Goldfrank. According to Temperley, Seymour in a private conversation had to push the Tsar to be more specific about the Ottoman Empire. Eventually, the Tsar stated,