We report a retrospective analysis of the clinical indications for 3555 penetrating keratoplasties performed at our department between 1971 and 1990. The cases were distributed among 12 diagnostic categories. Regrafting was the most common indication overall, accounting for 1452 cases (40.8%). Other major indications were, in order of decreasing frequency, keratoconus (17%), scarring secondary to herpes simplex keratitis (11.7%), aphakic bullous keratopathy (5.9%) and interstitial keratitis (5%). Further analysis of the relative percentages in each category within each 5-year interval of the study period was carried out to identify any changes in incidence. Viral disease as an indication for penetrating keratoplasty has shown a gradual decrease in frequency, accounting for only 6.4% of the cases during the last 5-year period (1986-90) compared with 19.6% during the first 5 years (1971-75). This finding is consistent with the marked improvement in the recognition and medical treatment of herpes simplex keratitis. The increase in incidence of grafting for pseudophakic bullous keratopathy in 1986-90 (6.7%) compared with 1981-85 (1.1%) correlates well with the dramatic increase in the number of cataract extractions with intraocular lens implantations performed during that period.