Variation in patients' preoperative co-morbidities can have a significant effect on the outcomes of cataract surgery. To examine the effects of that variation, we did a retrospective study of the outcomes of extracapsular cataract surgery performed by seven surgeons. Medical records from 791 surgeries done from June 1, 1986, through May 31, 1989, were retrospectively examined. Variations in postoperative visual acuity and intraoperative and postoperative complications were documented. The relationships between preoperative ocular and systemic medical co-morbidities and postoperative visual results and complications were studied. A statistical model was developed to adjust for the preoperative co-morbidity case mix between physicians. Visual acuity rates varied by surgeon and surgical volume, but not significantly when adjusted for patient case mix.