Retrospective analysis of 358 cases of retinoblastoma for correlation between age and intraocular stage at the time of diagnosis revealed: in both early and advanced stages of intraocular disease, bilateral retinoblastoma presents at an earlier age than does unilateral retinoblastoma; support for the Knudson "two-hit" hypothesis of retinoblastoma genetics, the existence of a positive family history for retinoblastoma does not guarantee an earlier age at diagnosis compared to sporadic disease; and for any age at diagnosis, unilateral or bilateral disease, Group V is the most common intraocular stage found.