BACKGROUND--The issue of seasonal variation of herpetic ocular infections is still controversial. This study was designed to examine whether this variation exists and can be defined as a significant circannual rhythm. METHODS--The patterns of recurrent attacks were monitored in 541 patients over a period of 15 years. Rhythm parameters were analysed according to age, sex, and clinical signs. RESULTS--The majority of herpetic eye attacks exhibited the highest peak in January (p < 0.04), except in the group of atopic children where the incidence of the disease peaked in September (p < 0.05). Among the various clinical forms, significant circannual periodicities were found only in the occurrence of epithelial herpetic keratitis (p < 0.03). The rhythms were detected among males (p < 0.03) but not among females. No direct correlation was demonstrated between the presence of the rhythms and the triggering effect of upper respiratory tract infections. CONCLUSIONS--Chronoepidemiological evaluation of individual reactivation patterns may be beneficial to certain patients and contribute to the optimisation of the treatment when prophylaxis is considered.