Germline mutations in the RB1 gene confer hereditary predisposition to retinoblastoma. We have performed a mutation survey of the RB1 gene in 232 patients with hereditary or non hereditary retinoblastoma. We systematically explored all 27 exons and flanking sequences as well as the promotor. All types of point mutations are represented and are found unequally distributed along the RB1 gene sequence. In the population we studied, exons 3, 8, 18 and 19 are preferentially altered. The range of frequency of detection of germline mutations is about 20%, indicating that other mechanisms of inactivation of RB1 should be involved. The spectrum of mutations presented here should help to improve the clinical management of retinoblastoma and to understand the molecular mechanisms leading to tumorigenesis.