Femoral varus osteotomy is an established therapy for Legg-Calvé-Perthes disease. The amount of surgical varus angulation is usually measured as the difference between the preoperative and the postoperative projected femur neck-shaft angle. We developed a more accurate measurement technique that considers changes of leg position and assessed the surgical varus angulation on two postoperative radiographs of each of 65 uniplanar femoral varus osteotomies. The mean difference between both surgical varus angulation measurements was 2.0 degrees +/- 1.4 degrees (range 0.0-5.0 degrees), the Pearson's correlation result was r = 0.96. The mean surgical varus angulation was 18.7 degrees +/- 7.3 degrees (range -2.5 to 43.5 degrees). Comparison with the preoperatively planned angulation showed a mean difference of 6.6 +/- 5.2 degrees (range 0.25-22.5 degrees).