Microphthalmos occupies a spectrum from a normal, but small globe, to a globe with multiple anterior and posterior segment abnormalities. This study examines 54 eyes of 27 patients who had bilateral microphthalmos and severe visual impairment or blindness. Congenital cataract was the commonest cause of severe visual impairment (44%), followed by presumed retinal or optic nerve dysplasia (30%) and chorioretinal coloboma (22%). Lensectomy was followed by phthisis bulbi in 3/23 cases and retinal detachment in 2/23 cases. There were no cases of angle closure glaucoma. The three clinical conditions associated with a poor prognosis were cataract, chorioretinal coloboma, and a markedly reduced corneal diameter. A corneal diameter of 6 mm or less was associated with a visual acuity of no perception of light in 81% (21/26) compared with 4% (1/28) of those with larger corneas.