We determined whether a PACS-based method (head-lesser trochanter distance [HLD]) better equalized leg length discrepancy (LLD) after primary THA than a conventional method. We retrospectively reviewed 312 patients (379 hips) with osteonecrosis or primary osteoarthritis who underwent primary cementless THA: 198 patients (240 hips) underwent THA using the HLD method, while the conventional group consisted of 114 patients (139 hips) in whom we measured with the method of McGee and Scott. We then compared the LLDs in the two groups. We observed no difference in the mean postoperative LLD. A higher percentage of patients in the HLD group had an LLD less than 6 mm: 81% vs 68% hips, respectively. HLD method decreases the possibility of an LLD over 6 mm after THA.