PURPOSE: In 40% retinoblastoma (Rb) results from a hereditary mutation of the Rb susceptibility gene (RB1). In this study, we tested the usefulness of intragenic DNA analysis for ophthalmologic follow-up in affected families. METHODS: Molecular analysis was performed on 103 DNA samples of 15 Rb families. We used 7 intragenic polymorphic markers and one within the ESD gene for mutation linkage analysis. FINDINGS: DNA analysis was informative in 88% of relatives at risk of developing Rb. Among them, the presence of a mutated RB1 allele was excluded in 46%, while 29% were unaffected carriers and 25% had inherited the Rb predisposition. CONCLUSION: In the majority of familial Rb, the DNA analysis allows the identification of children carrying a RB1 mutation and who will need a close ophthalmologic follow-up under general anesthesia. When the mutated gene is absent, ophthalmological examination under narcosis is unnecessary. Finally, identification of asymptomatic carriers improve the accuracy of genetic counselling.