Purpose: To analyze the outcome of metatarsal lengthening of first brachymetatarsia by callotasis using an external fixator. Materials and Methods: Between January 1998 and February 2004, 10 patients (17 cases) were reviewed. The mean age at operation was 17.3 years. Seven patients had bilateral first brachymetatarsia and eight patients had combined 4th brachymetatarsia. The operations were performed with a monoexternal fixator, and distraction was started at a rate of 0.75 mm/day after 7 days. The radiographic results were evaluated by lengthening amount and percentage, fixation time, and healing index. Complications and AOFAS score were evaluated. Results: The average lengthening amount was 17.7 mm and the average lengthening percentage was 43.4%. The external fixation time was 107 days and average healing index was 69.8 days/cm. The evaluation according to AOFAS score was excellent in 12 cases and good in 5 cases. Complications were 4 cases of hallux valgus, 4 of metatarsophalangeal joint stiffness, 3 of medial angular deformity, 3 of pes cavus, 2 of pin breakage, 2 of pin site infection, and 1 of skin hyperpigmentation. Conclusion: Callotasis for 1st brachymetatarsia is a very useful treatment method with high patient satisfaction, excellent healing rate and early ambulation without bone graft. Nevertheless, great care must be taken to minimize the various possible complications.