Retinoblastoma (RB) is a malignant childhood tumor that results from loss or inactivation of both alleles of the RB1 gene. Human papillomavirus (HPV) DNA sequences have been found in RB tissue, suggesting a role of the viral infection with RB. We here describe a child with disseminated bilateral RB without familial history, who displayed a loss of material from 10p. Fluorescence in situ hybridization studies showed a somatic loss of both alleles of the RB1 gene. Moreover, sequences for HPV-6a were detected on DNA extracted from eye tumor tissue and from nonstimulated peripheral blood leukocyte cultures. The eye tumor tissue was also positive for HPV L1 viral proteins. Repeated loss of the short arm of chromosome 10 in HPV-transfected keratinocytes has been reported. Loss of heterozygosity in 10p14 approximately p15 is also frequent in cervical cancers. Therefore, it seems probable that the abnormalities on 10p detected in the present case are related to the HPV infection. Thus, HPV could be a cofactor in the progression of RB by promoting nonrandom additional mutations.