The clinical features of herpes simplex keratitis seen in 370 eyes of 356 patients (211 males and 145 females) in the outpatient clinic of the Yokohama City University hospital during the last 30 years (1963-1992) were statistically analyzed. The age of patients ranged from 1 to 75 years (mean 38.4 years). Bilateral herpetic keratitis was seen in 11 patients (10.4%) in the period of 1980-1992. Epithelial keratitis, stromal keratitis, and corneal endotheliitis were observed in 67 patients (57.3%), 46 patients (39.3%), and 4 patients (3.4%), respectively, in the period of 1980-1992. There was no significant change in the incidence of the types of corneal lesions during the last 13 years as compared with those in the previous 17 years (1963-1979). Life-table analysis revealed that 5-year recurrence rates were 17.5% in patients treated with acyclovir (ACV) and 52.9% in those treated with idoxuridine (IDU). The recurrence rate in ACV-treated patients was significantly lower than that in IDU-treated patients. Severe cases, such as those complicated by deep corneal ulcers with hypopyon, descemetoceles, or necrotizing keratitis, were decreased in number in ACV-treated patients, as compared with IDU-treated patients.