We studied personality traits of patients with keratoconus in a controlled prospective study using the Minnesota Multiphasic Personality Inventory (MMPI). Whereas four of 16 (25%) control patients with herpes simplex keratitis had scores indicative of psychological abnormality, 15 of 28 (54%) keratoconus patients had scores indicative of abnormality (P less than .05). Keratoconus patients who had undergone penetrating keratoplasty had a lower rate of abnormal scores (3 of 9; 33%) than unoperated keratoconus patients (12 of 19; 63%) (P less than .05). Patients who considered themselves moderate or severely limited by their eye condition were more likely to have abnormal scores (7 of 8; 87%) than patients who thought they were mildly affected (8 of 20; 40%) (P less than .05).