There have been few reports of shortening of the first ray of the foot because of damage to the physis of the first metatarsal during the performance of metatarsal osteotomy for residual metatarsus adductus. In a retrospective study of twenty-seven feet in twenty patients who underwent this procedure, eight feet in seven patients were noted to have some degree of residual shortening of the first ray. This is an incidence of 30 per cent. The follow-up period after osteotomy ranged from two years to seven years and four months (average, four years). We could find no clear correlation between the occurrence of shortening and the patient's age at osteotomy, sex, or race, or the etiology of the adduction for which the osteotomy had been done. A clear correlation was found, however, with the surgical technique that had been employed. In two of the eight feet with a short first ray, the osteotomy had been done within the physis of the first metatarsal. In the other feet the procedure had employed an osteotomy site close to the physis or extensive periosteal dissection, or both. The results in our patients implicate subperiosteal dissection of the first metatarsal as an important, previously unreported cause of damage to the physis and of the resultant shortening. We recommend radiographic determination of the relationship of the osteotomy site to the physis before dissection is performed.