BACKGROUND: A retrospective analysis of all patients with retinoblastoma on file at the Ophthalmic Oncology Center of the New York Hospital, Cornell University Medical Center was performed to examine the characteristics of retinoblastoma in children with a unilaterally affected parent. METHODS: Data were analysed for laterality of disease, age at initial diagnosis, number of tumour foci at diagnosis, ocular outcome, and patient survival. RESULTS: There were 54 patients, including nine pairs of siblings, diagnosed with retinoblastoma, each of whom had one unilaterally affected parent. The retinoblastoma was bilateral in 49 (91%) patients and unilateral in the remaining five (9%). The mean age at diagnosis was 10.5 months (range 1-36 months) and 35 patients (65%) were diagnosed within the first year of life. The mean number of initial tumour foci was 1.7 per eye; 1.6 foci per eye in bilaterally affected patients, and 3.7 foci per eye in unilaterally affected patients (p = 0.36). Retention of the eye was possible for 51 of 103 eyes affected with retinoblastoma. The mean follow up for patients was 9.0 years, with a range of 1 month to 30.5 years. There were a total of 12 deaths (22%): from retinoblastoma (two), sarcoma (five), cutaneous malignant melanoma (one), cancer type unknown (two), and cause unknown (two). CONCLUSION: Overall, the characteristics of retinoblastoma patients with a unilaterally affected parent, were similar when compared with all retinoblastoma patients with a positive family history.