To compare costs of molecular and conventional screening of retinoblastoma relatives, we evaluated the direct health care costs. With variables set at the most likely values (baseline), the expected cost (in 1994 Canadian dollars) of conventional screening was $31,430 for a prototype family consisting of seven at-risk relatives (three clinic exams and eight examinations under anaesthetic over the first 3 years of life for each relative). For the molecular strategy that involves looking for the RB1 gene mutation in the proband, testing the relatives for that mutation, and clinical follow-up similar to conventional strategy for relatives with mutation, the expected cost was $8,674, using baseline variables. Sensitivity analysis over the range of values for each variable revealed a significant saving of health care dollars by the molecular route, indicating the benefit of redirecting economic resources to molecular diagnosis in retinoblastoma.