Study of case-notes and autopsy reports of patients with renal disease suggests that analgesic nephropathy is responsible for at least 12 per cent of cases of chronic renal failure, Between 1970 and 1975 eight new cases of analgesic nephropathy were seen annually in a population of three-quarters of a million. This is equivalent to an incidence of 490 new cases per year in England and Wales. Fifty-five patients with analgesic nephropathy were followed from one to 84 months for a total of 190 patient years. Changes in renal function were correlated with bacteriuria, hypertension and analgesic consumption. One-third of the cases had been misdiagnosed and analgesic abuse was only revealed by thorough examination of case-notes and autopsy records, together with careful questioning of patients and relatives. A number of cases had been classified as chronic pyelonephritis. The calculated survival rate at five years was 44 per cent. Mortality was related to the level of analgesic consumption and the degree of renal failure at the time of diagnosis. The prognosis was poor if serum creatinine at presentation was greater than 400 mumol/l. There was no significant correlation between deterioration in renal function and bacteriuria or hypertension. Forty-two per cent of the patients were taking analgesics for arthritis; 27 per cent had rheumatoid arthritis. Most had been taking large quantities of analgesic mixtures containing phenacetin. Renal papillary necrosis was present in only 26 per cent on intravenous urography but was found in all those examined at autopsy. Twenty thousand, two hundred and twenty-nine autopsy reports were examined for the presence of renal disease. Renal papillary necrosis was found in 0.41 per cent, and could be attributed to analgesic nephropathy in 24 per cent. In patients under 65 years of age analgesic nephropathy appeared to be a more frequent cause of death than chronic pyelonephritis. The report indicates the need for careful enquiry about analgesic consumption in all patients with renal disease, and emphasizes the importance of early diagnosis and cessation of analgesics in suspected cases of analgesic nephropathy.