The correct diagnosis of proliferation diabetic retinopathy is essential, because it is a treatable disease and missing the diagnosis can lead to the patient becoming blind. We examined the ability of internists and ophthalmologists to diagnose proliferative retinopathy under optimal conditions. Twenty-three physicians performed retinal examinations on ten diabetic patients and one normal patient with dilated pupils. Physician examiners were members of a university medical center and included 10 internists, 2 diabetologists, 4 senior medical residents, 4 general ophthalmologists, and 3 ophthalmologists who were subspecialists in retinal disease. Correct diagnosis was determined separately by the consensus of three ophthalmologists specializing in retinal disease, who reviewed seven-view stereo fundus photographs and medical charts. Of a possible 483 individual eye a examinations, 438 were completed. The overall error rate was 61%. The error rate for missing the diagnosis of proliferative retinopathy varied from 0% for retinal specialists to 49% for internists, diabetologists, and medical residents. We conclude that potentially serious mistakes in diagnosis are currently made by the physicians who care for most diabetic patients. Experience and specialized knowledge lessen that the error rate. Further education or greater use of referrals may be necessary to provide optimal patient care.