p53 was examined by immunohistochemistry in five cases of retinoblastoma, a neoplasm that is caused by a loss of function of the Retinoblastoma susceptibility gene (Rb), mapped to chromosome 13q14. Object of the study was the identification of eventual further gene mutation in retinoblastoma tumor cells determining the onset of an independent tumoral monoclonal cell subset. We did not observe any positive reaction for p53 protein expression in the five cases we analyzed.