Retinoblastoma is a cancer of the retina that occurs in young children, in the majority of cases initiated by mutations in the RB1 tumour suppressor gene. About 40% of retinoblastoma patients have a germline RB1 mutation which gives them a hereditary predisposition to develop retinoblastoma. Knowledge of the presence of an RB1 mutation can help in clinical care and family planning. The Dutch National Retinoblastoma Register collects information on all Rb patients diagnosed in the Netherlands. In this paper the authors describe the results of RB1 mutation scanning in 529 Dutch retinoblastoma patients from 433 independent families from the Register. We detected an RB1 mutation in 92% of familial and non-familial bilateral patients. A total of 187 RB1 germline mutations were found, including 33 novel mutations. Several three-generation families with incomplete penetrance RB1 mutations are described. (By Berber Mol, http://jmg.bmj.com/content/early/2014/03/31/jmedgenet-2014-102264 )