This study examined long-term cause-specific mortality among 998 Dutch retinoblastoma survivors, diagnosed from 1862 to 2005, according to follow-up time, treatment and heredity. After a median follow-up of 30.8 years, only cause-specific mortality for second malignancies among hereditary retinoblastoma survivors was statistically significantly increased with 12.8-fold. Risk of death from second malignancies among non-hereditary survivors was not increased. Mortality rates of second malignancy among hereditary patients were non-significantly elevated with 1.6-fold for treated with radiotherapy, compared to those treated otherwise. Standardised mortality ratios (SMRs) for second malignancy among hereditary patients increased during the first three decades after retinoblastoma diagnosis. Whereas these risks decreased after three decades, the absolute excess risk (AER) increased significantly, up to 23.2 excess cases per 1000 patients/year after five decades of follow-up. Fifty years after retinoblastoma diagnosis the cumulative mortality from any second malignancy was 17.3% for hereditary patients. Very long-term follow-up of retinoblastoma patients revealed an emerging excess risk of mortality in hereditary retinoblastoma survivors. This implies that lifelong follow-up is needed, whereas at the same time, patients and their physicians must be alerted to the increased second malignancy risks.