Interstitial nephritis, also known as tubulointerstitial nephritis, is inflammation of the area of the kidney known as the renal interstitium, which consists of a collection of cells, extracellular matrix, and fluid surrounding the renal tubules. It is also known as intestinal nephritis because clinical picture is showing mesenteric lymphadenitis in such cases of acute pyelonephritis (mostly due to use of NSAIDs). More specifically in case of recurrent urinary tract infection secondary infection can spread to adjacent intestine. In addition to providing a scaffolding support for the tubular architecture, the interstitium has been shown to participate in the fluid and electrolyte exchange as well as endocrine functions of the kidney.

There are a variety of known factors that can provoke the inflammatory process within the renal interstitium, including pharmacologic, environmental, infectious and systemic disease contributors. The spectrum of disease presentation can range from an acute process to a chronic condition with progressive tubular cell damage and renal dysfunction.