Retinoblastoma (Rb) is the most common primary intraocular malignancy in children. It is brought about by the mutational inactivation of both alleles of RB1 gene in the developing retina. To identify the RB1 mutations, we analysed 74 retinoblastoma patients by screening the exons and the promoter region of RB1. The strategy used was to detect large deletions/duplications by fluorescent quantitative multiplex PCR; small deletions/insertions by fluorescent genotyping of RB1 alleles, and point mutations by PCR-RFLP and sequencing. Genomic DNA from the peripheral blood leucocytes of 74 Rb patients (53 with bilateral Rb, 21 with unilateral Rb; 4 familial cases) was screened for mutations. Recurrent mutations were identified in five patients with bilateral Rb, large deletions in 11 patients (nine with bilateral Rb and two with unilateral Rb), small deletions/insertions were found in 12 patients all with bilateral Rb, and point mutations in 26 patients (14 nonsense, six splice site, five substitution and one silent change). Three mutations were associated with variable expressivity of the disease in different family members. Using this method, the detection rates achieved in patients with bilateral Rb were 44/53 (83%) and with unilateral Rb, 5/21 (23.8%). This approach may be feasible for clinical genetic testing and counselling of patients.