Causal relationships between ulnar variance and wrist disorders are known ' Gripping and pronation cause proximal translation of the radius with respect to the ulna, leading to a statistically significant increase In ulnar variance. The purpose of this study was to investigate variation of the ulnar variance with powerful grip. A total of 41 male volunteers aged between 19 and 25 years (mean, 21.2 +/- 1.7 years) were studied. Posteroanterior X-ray films of all wrists were taken in the standardized position. After neutral posteroanterior X-ray films had been taken, subjects were asked to grip a Takei hand dynamometer with maximum force while repeated standardized posteroanterior X-ray films were obtained. Ulnar variance values were measured using the perpendicular method. Mean maximum grip force was 38.1 kg (range, 26.6-47.9 kg). Mean values of force-free (neutral) and forced u1nar variances were 0.06 +/- 0.21 mm and 1.87 +/- 10.23 mm, respectively. The difference in u1nar variance between the two groups was statistically significant (P < 0.00 1). The increase in u1nar variance with grip observed varied between 0.00 mm (minimum) and 3.97 mm (maximum), with a mean of 1.81 mm. Gaining an understanding of normal limits of u1nar variance modification with grip may be helpful in planning surgical treatment. The French version of this article is available in the form of electronic supplementary material and can be obtained by using the Springer Link server located at http://dx.doi.org/10.1007/s00276002-0033-6.