Background: Survivors of hereditary retinoblastoma have an elevated risk of developing second malignancies, but data on the risk in middle-aged retinoblastoma survivors (ie, those with more than 40 years of follow-up) are scarce. Methods: Data from the Dutch retinoblastoma registry were used to analyze risks of second malignancies in 668 retinoblastoma survivors, diagnosed from 1945 to 2005 (median age = 24.9 years) and classified as having had hereditary or nonhereditary disease based on the presence of family history, bilateral disease, or a germline RB1 mutation. Standardized incidence ratios (SIRs) and absolute excess risks (AERs) of subsequent cancers in patients with hereditary and nonhereditary disease were estimated by comparison with Dutch sex-, age-, and calendar year-specific rates. Multivariable Cox regression and competing risk analyses were used to determine associations of treatment with risks of second malignancies. All statistical tests were two-sided. Results: After a median follow-up of 21.9 years, the risk of second malignancies in survivors of hereditary retinoblastoma (SIR = 20.4, 95% confidence interval [CI] = 15.6 to 26.1) far exceeded the risk of survivors of nonhereditary retinoblastoma (SIR = 1.86, 95% CI = 0.96 to 3.24). Among patients with hereditary disease, treatment with radiotherapy was associated with a further increase in the risk of a subsequent cancer (hazard ratio = 2.81, 95% CI = 1.28 to 6.19). After 30 years of follow-up, elevated risks of epithelial cancers (lung, bladder, and breast) were observed among survivors of hereditary retinoblastoma. After 40 years of follow-up, the AER of a second malignancy among survivors of hereditary retinoblastoma had increased to 26.1 excess cases per 1000 person-years. The cumulative incidence of any second malignancy 40 years after retinoblastoma diagnosis was 28.0% (95% CI = 21.0% to 35.0%) for patients with hereditary disease. Conclusion: Our analysis of middle-aged hereditary retinoblastoma survivors suggests that these individuals have an excess risk of epithelial cancer. Lifelong follow-up studies are needed to evaluate the full spectrum of subsequent cancer risk in hereditary retinoblastoma survivors. © The Author 2008. Published by Oxford University Press.