364 eyes from 230 patients with retinoblastoma diagnosed and treated at the Lausanne University Eye Clinic from 1964 to June 1994 were retrospectively analyzed with respect to the risk of developing new tumour foci following initial therapy. Among them, 119 eyes from 90 hereditary affected patients were included, consisting of 86 bilateral cases and 4 unilateral cases. The mean follow-up was 65.5 months (5.5 years). A total of 46 new retinal tumours were detected in 21 patients. These new tumours had a size less than 1 disc diameter in 75% and were peripherally located in 78% of the cases, with a statistically significant preference for the horizontal meridians. No new tumours developed in the macular area. 50% appeared in children younger than 1 year and 80% before 2 years of age. 50% of the eyes with recurrences developed new tumours before 7.5 months following diagnosis, and 75% before 14 months. All patients showing recurrences did so before the age of 4.5.