Differential diagnosis and histopathological findings of bilateral congenital retinal detachment in a 10-month-old boy are presented. By ultrasonography, the presence of bilateral retinoblastoma was suspected. Histopathological examination of the more seriously affected eye revealed retrolental mass composed of tightly packed retinal folds fused together by fibrovascular tissue. The retina was partly disorganized, with the ganglion cells scanty or missing. Large retinoschisis cysts were not found, but areas of splitting in the inner retina were present. Examination of the family members disclosed congenital retinoschisis in the maternal grandfather and his two brothers. These findings indicate that the most probable etiology of bilateral congenital retinal detachment of the patient was hereditary X-linked retinoschisis. Surgery for retinal detachment of the fellow eye was not successful.