Ulnar variance was measured in 325 normal wrists and 41 wrists with Kienböck's disease. A positive correlation between ulnar variance and age was confirmed in normal wrists, and it was lower in males than in females. Therefore, studies comparing ulnar variance in abnormal and normal wrists require carefully selected age- and sex-matched controls. There was no significant difference in ulnar variance between Japanese with normal wrists and those affected by Kienböck's disease, when the effects of sex and age were taken into account. Based on these results, we believe that ulnar variance is highly unlikely to be an important predisposing factor in Kienböck's disease.