Since there have been recent isolated reports of retinoblastoma associated with chromosomal defects, karyotypes were performed on 21 retinoblastoma patients (17 sporadic, 4 hereditary) in an attempt to associate a specific chromosomal abnormality with this disease. Chromosomes from a family with hereditary retinoblastoma were also studied using the new technique of scanning electron microscopy. No abnormalities were detected.