The development of an in vivo model of retinoblastoma could be important for studying its biological behaviour and developing novel therapeutic strategies. We examined the ability of patient-derived retinoblastoma cells to grow and disseminate in severe combined immunodeficiency CB-17-SCID mice after subcutaneous (s.c.) inoculation without conditioning treatment. 24/30 (80%) of patient-derived tumours engrafted and grew as s.c. nodules in SCID mice. Whilst most xenografted tumours appeared to be localised, by PCR assay a positive DNA band of human minisatellite region (YNZ.22) was determined in the bone marrow of 19/25 (76%), in the spleen of 14/25 (56%) and in the liver of 16/25 (64%) mice, respectively, indicating dissemination to distant organs. Cytogenetic analysis demonstrated i(6p) in 5/12 (42%) and trisomy 1 or 1q abnormalities in 8/12 (67%) of the xenografted tumour samples studied, respectively, suggesting that retinoblastoma tumour cells maintain their cytogenetic abnormalities following adoptive growth in SCID mice. In this report we demonstrate the ability to propagate human primary retinoblastoma cells in SCID mice after s.c. inoculation and suggest the possibility of using the SCID mouse model to study the intrinsic biological behaviour of human retinoblastoma and to develop novel therapeutic strategies in the treatment of this disease.