A retrospective analysis of 65 unilateral retinoblastoma patients treated initially with external beam radiation, revealed that 25 eyes (38.5%) developed local recurrence of retinoblastoma. The mean age at diagnosis was 1.8 years for patients who developed recurrences vs. 0.9 years for those who did not. Ninety-six percent of the recurrences occurred less than two years from the age at diagnosis; the amount of time from the end of external beam radiation treatment until a tumor recurred was independent of the age at diagnosis. The initial largest basal diameter was 10.7 DD for tumors which later recurred and 5.9 DD for tumors that were cured. Sixty-nine percent of eyes in groups III-V had tumor recurrence, and 10% of eyes in groups I-II had recurrence. All but one eye (24 eyes) that developed recurrence were enucleated. Family history of retinoblastoma, location of the tumor, gender, and laterality did not significantly correlate with the mean age of initial diagnosis for tumors that recurred or the mean time of onset for recurrence.