We have studied the concept of posterior condylar offset and the importance of its restoration on the maximum range of knee flexion after posterior-cruciate-ligament-retaining total knee replacement (TKR). We measured the difference in the posterior condylar offset before and one year after operation in 69 patients who had undergone a primary cruciate-sacrificing mobile bearing TKR by one surgeon using the same implant and a standardised operating technique. In all the patients true pre- and post-operative lateral radiographs had been taken. The mean pre- and post-operative posterior condylar offset was 25.9 mm (21 to 35) and 26.9 mm (21 to 34), respectively. The mean difference in posterior condylar offset was + 1 mm (-6 to +5). The mean pre-operative knee flexion was 111 degrees (62 degrees to 146 degrees) and at one year postoperatively, it was 107 degrees (51 degrees to 137 degrees). There was no statistical correlation between the change in knee flexion and the difference in the posterior condylar offset after TKR (Pearson correlation coefficient r = -0.06, p = 0.69).