Three brothers were found to have nanophthalmos as evidenced by marked hyperopia, decreased global axial length, and shallow anterior chambers. The thickness of the lens, measured with A-scan ultrasound biometry in two cases, was much greater than normal. Choroidal thickening with shallow retinal detachments without breaks was found in those patients. Fluorescein angioscopy demonstrated leaks beneath the serous retinal detachments in one. The spontaneous presence of choroidal effusions and retinal detachments in nanophthalmic patients has been reported only rarely. The present findings emphasize that careful examination of the posterior segment should be done prior to anterior segment surgery in these patients to alert the surgeon to the possibility of serious intra- and post-operative choroidal effusions and retinal detachments. An attempt is made to explain some of the clinical findings in nanophthalmos by extrapolating from results obtained on experimental animals. It is postulated that the increased lens size in nanophthalmos may be due to the abnormal accumulation of a factor influencing lens fiber differentiation. The overall small size of the eye may be the result of the formation of a smaller than usual optic vesicle anlage.