A retrospective study of 79 secondary intraocular lens implants performed during 1984-87 in a large teaching hospital is reported. The period of follow-up ranged from 6 months to 3.9 years (mean 16.6 months). The principal indication for surgery was contact lens intolerance. Thirty-four per cent of the patients had previously undergone cataract surgery with implantation of the other eye. Eighty-three per cent of the patients achieved a visual acuity within one Snellen line of best-corrected preoperative visual acuity. A further 2.5% lost two lines of Snellen chart acuity, and 14.5% had a substantial reduction in visual acuity. We conclude that in carefully selected patients secondary intraocular lens implantation is an acceptable and often highly successful way of treating monocular aphakia and we discuss the selection and preoperative investigation of such patients.