Kidney diseases, or renal diseases, technically referred to as nephropathies, are pathological conditions affecting the kidneys—the organs that facilitate removal of waste products and toxins from the bloodstream, regulate the body's concentration of electrolytes, maintain the appropriate acid-base balance of plasma, and produce urine as a byproduct of metabolism.

When used colloquially, the term kidney disease may refer to chronic kidney disease (CKD), an umbrella term for any progressive loss of kidney function over at least three months, from any cause. In contrast, kidney damage over a shorter period of time is known as acute kidney injury.

From a technical standpoint, the heterogenous group of kidney diseases is heterogenous can be broadly divided into categories based on which anatomical structures are involved: the glomeruli, the filtering capillaries of the kidney; tubules, which carry filtered blood; the renal interstitium, the fluid-filled space between these structures; and the renal blood vessels, which deliver blood towards and away from the kidney. Glomerular disease, or glomerulonephritis, can be further divided into the nephritic and nephrotic syndromes, which are respectively characterized by blood and protein leaking into the urine.

All forms of kidney disease, glomerular or otherwise, have the potential to damage all four components of the kidney, culminating in end-stage renal disease—the stage of disease at which dialysis or a kidney transplant are necessary.

Rates for both chronic kidney disease and mortality have increased, associated with the rising prevalence of diabetes and the aging global population. The World Health Organization has reported that "kidney diseases have risen from the world's nineteenth leading cause of death to the ninth, with the number of deaths increasing by 95% between 2000 and 2021." In the United States, prevalence has risen from about one in eight in 2007, to one in seven in 2021.

Causes of kidney disease include deposition of the Immunoglobulin A antibodies in the glomerulus, administration of analgesics, xanthine oxidase deficiency, toxicity of chemotherapy agents, and a long-term exposure to lead or its salts. Chronic conditions that can produce nephropathy include systemic lupus erythematosus, diabetes mellitus and high blood pressure (hypertension), which lead to diabetic nephropathy and hypertensive nephropathy, respectively.

One cause of nephropathy is the long term usage of pain medications known as analgesics. The pain medicines which can cause kidney problems include aspirin, acetaminophen, and nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and naproxen. This form of nephropathy is "chronic analgesic nephritis", a chronic inflammatory change characterized by loss and atrophy of tubules and interstitial fibrosis and inflammation (BRS Pathology, 2nd ed.).

Specifically, long-term use of the analgesic phenacetin has been linked to renal papillary necrosis (necrotizing papillitis).