['Controversy exists as to whether polyethylene (PE) penetration of hip prostheses is underestimated when the measurements are made on radiographs obtained in supine position as compared to weight-bearing position.', 'We examined 111 patients by radiostereometric analysis (RSA) in the supine and weight-bearing positions.', 'The mean 3-D penetration was 0.68 mm (SD 0.58, range 0.04-3.05) for the supine position and 0.70 mm (SD 0.57, range 0.08-3.01) for the weight-bearing position. The correlation between supine and weight-bearing examinations was 0.99 (p < 0.001). The degree of penetration made no difference. There was no statistically significant difference as to whether the first examination was performed early, i.e. after 3 months, or after 12 months (p = 0.7).'] Are weight bearing radiographs necessary for measurement of polyethylene penetration in total hip prostheses : a radiostereometric study of 111 patients examined in weight-bearing and supine position?