The authors follow conservative treatment of infantile trigger thumb because of the possible anesthetic and postoperative complications. Their conservative treatment involves passive exercise of the affected thumb performed only by the mother. Eighty-six percent of our patients showed improvement, with an average treatment period of 3 years 2 months. A secondary complication, radial flexion deformity of the distal phalanx at the affected thumb, was detected in 5% of patients. This secondary deformity occurred at an average age of 3 years 11 months. The authors think surgical release should be performed if any sign of such a deformity is noted. However, because none of the patients with the complication felt this was a cosmetic problem, the authors have not experienced a case for which the patient desired surgery. Although conservative treatment tends to require a long period of time, the authors consider it to be a useful method.