Chronic tubulointerstitial nephritis is usually asymptomatic, presenting with slowly progressive renal impairment. Urinalysis may be normal or show low-grade proteinuria (<1.5 g/day) and/or pyuria. Diagnosis depends on renal biopsy, which reveals variable cellular infiltration of the interstitium, tubular atrophy, and fibrosis. There are many causes including sarcoidosis, drugs (prescribed and nonprescribed), irradiation, toxins, and metabolic disorders. Analgesic nephropathy—characterized by renal papillary necrosis and chronic interstitial nephritis and caused by the prolonged and excessive consumption of combinations of analgesics, mostly including phenacetin. Nonsteroidal anti-inflammatory drugs—the most frequent cause of permanent renal insufficiency after acute interstitial nephritis. Aristolochic acid nephropathy—(1) Chinese herb nephropathy—caused in most cases (but perhaps not all) by aristolochic acid, and is associated with a high incidence of urothelial malignancy. (2) Balkan endemic nephropathy—a chronic, familial, noninflammatory tubulointerstitial disease of the kidneys that is associated with a high frequency of urothelial atypia, occasionally culminating in tumours of the renal pelvis and urethra. 5-Aminosalicylic acid—used in the treatment of chronic inflammatory bowel disease and causes clinical nephrotoxicity in approximately 1 in 4000 patients/year. Chronic interstitial nephritis in agricultural communities (CINAC) —nonproteinuric chronic kidney disease that presents in young, agricultural workers in Central America and Sri Lanka in the absence of any clear aetiology. Lithium—the most common renal side effect is to cause nephrogenic diabetes insipidus. Radiation nephropathy—preventive shielding of the kidneys in patients receiving radiation therapy generally prevents radiation nephropathy, but total body irradiation preceding bone marrow transplantation leads 20% to develop chronic renal failure in the long term. Nephropathies induced by toxins (including lead and cadmium) or by metabolic disorders (chronic hypokalaemia and chronic urate nephropathy).