Rb-1 gene promoter mutations are very rare events, only three retinoblastoma families with such alterations were reported up to now. Herein, we describe the first case of the Rb-1 gene promoter germ, line de novo mutation in a proband with sporadic unilateral retinoblastoma. All of reported Rb-1 gene promoter mutations are associated with a reduced penetrance. Together with the literature data it can be roughly estimated that penetration of cases with alteration localised in promoter and similar as in presented case, is at the level of about 60-70%. It seems, that there are some promoter sites more prone for occurrence of mutations.