Diclofenac is a nonsteroidal anti-inflammatory drug approved in the United States in 1988 for the treatment of patients with osteoarthritis, rheumatoid arthritis, or ankylosing spondylitis. To characterize the clinical, biochemical, and histological features and possible mechanisms of hepatic injury associated with its use, a retrospective analysis was undertaken of 180 patients whose cases were reported to the Food and Drug Administration from November 1988 through June 1991, as having had possible adverse reactions to diclofenac. Of the reported 180 cases, 79% were female, 71% were 60 years of age or older, and 77% had osteoarthritis. Sixty-seven percent of the cases were detected by symptoms and the remainder by abnormal laboratory tests. Seventy-five percent of the symptomatic patients (90 of 120) were jaundiced. Seven of the 90 icteric patients died. The biochemical pattern of injury was hepatocellular or mixed hepatocellular in 66% of cases. Only 8% had a pattern of cholestatic injury. The remainder, with modestly increased values of both transaminases and alkaline phosphatase, were considered "indeterminate," i.e., either mild hepatocellular or anicteric "cholestatic" injury. Sections of liver from 21 cases were available for study. Hepatic injury was apparent by 1 month after starting the drug in 24%, by 3 months in 63%, and by 6 months in 85% of cases. The latent period in 12% was 6 to 12 months, whereas in 3% it was greater than 12 months.(ABSTRACT TRUNCATED AT 250 WORDS)