Lateral column lengthening procedures are typically performed in patients with flatfoot deformity. There have been reports of complications caused by lateral column lengthening. In this study, clinical and radiographic osteoarthritis of the fourth and fifth tarsometatarsal joints were retrospectively assessed as complications after lateral column lengthening. Seventeen stage II flatfeet belonging to 15 patients were included. The mean age of the subjects was 64.2 ± 7.7 (range 52-80) years. The average lateral column lengthening length achieved was 12.7 ± 2.2 (range 8-15) mm. The average duration of follow-up postsurgically was 57.2 ± 37.7 (range 4-110) months. The pain group (n = 8), who postoperatively experienced weightbearing pain in the plantar-lateral aspect of the foot and/or tenderness at the dorsal-lateral, and the no-pain group (n = 9) were compared. All patients in the pain group underwent lateral column lengthening of 10 mm or more. However, there were no significant differences in age, body mass index, American Orthopaedic Foot and Ankle Society score, and the lateral column lengthening amounts between the groups. In the pain group, all patients had osteoarthritic changes in the fourth and fifth tarsometatarsal joints. In all subjects, 11 feet were diagnosed osteoarthritis. Patients with pain had a significantly lower postoperative first talometatarsal angle (p ≤ .05). Osteoarthritis of the fourth and fifth tarsometatarsal joints as complications after lateral column lengthening in flatfoot is first reported. Our study indicated a high possibility of osteoarthritis in patients who had pain in the lateral aspect of the foot after lateral column lengthening.