The nature of the tumorigenic mutation was analyzed in 30 retinoblastoma (Rb) tumors (16 non-hereditary and 14 hereditary) and categorized into loss of heterozygosity (LOH) or retention of heterozygosity (non-LOH) at the RB1 locus. These genotypic characteristics were compared with the clinicopathological phenotype for possible correlation. The overall frequency of LOH was roughly 55%, in both hereditary and non-hereditary Rb. The presence of LOH was preferentially associated with differentiated tumors and absence of choroidal invasion. LOH was found in 82% of females versus 33% of males. Finally, LOH-initiated tumors were associated with a significantly younger age at diagnosis in hereditary Rb. In conclusion, the preferential association of LOH with absence of choroidal invasion, tumoral differentiation, and younger age at diagnosis may establish LOH as a prognostic marker in Rb patients.