This retrospective review of 814 retinoblastoma patients discloses 240 cases of tumor extension into the optic nerve. Optic nerve involvement was classified according to the degree of invasion; grade I is superficial invasion of the optic nerve head only, grade II is involvement up to and including the lamina cribrosa, grade III is involvement beyond the lamina cribrosa, and grade IV is involvement up to and including the surgical margin. The incidence of optic nerve involvement was 29.5% (240/814). The mortality rate of patients with optic nerve involvement with grade I was 10%; grade II, 29%; grade III, 42%; and grade IV, 78%. Actuarial life-table analysis shows an increased mortality rate with increasing grade of optic nerve involvement. Multivariate statistical analysis shows that the grade of optic nerve involvement and the age at diagnosis of optic nerve involvement are the factors most significantly associated with survival.