PURPOSE: To report unilateral pupil-sparing third nerve palsy after use of sildenafil citrate (Viagra). METHOD: Case report. RESULTS: A 56-year-old man with a history of tobacco abuse was treated for erectile dysfunction, Viagra, 50 mg, was taken once without adverse effect. Three weeks later, the patient took a second dose of Viagra (50 mg); 36 hours later he experienced a complete pupil sparing third nerve palsy. Erythrocyte sedimentation rate, blood glucose level, magnetic resonance imaging, and magnetic resonance angiography were normal. CONCLUSION: In a patient with microvascular disease, use of sildenafil may be associated with pupil sparing third nerve palsy. (C) 1998 by Elsevier Science Inc. All rights reserved.