We report a splint system for a protected mobilization program (termed dynamic treatment) of proximal phalangeal fractures. This program can be used for nonoperative treatment or after operative treatment. Intra-articular fractures of the proximal phalanx at the metacarpophalangeal joint were included. The custom-molded 2-component thermoplastic splint allows motion of the proximal and distal interphalangeal joints. It was developed to allow bone healing and recovery of motion at the same time. We evaluated the clinical and radiologic results of a consecutive series of 48 displaced proximal phalangeal fractures in 45 patients who received dynamic treatment. Fracture consolidation was achieved in all patients and bone healing and recovery of full active motion was achieved simultaneously in all but 4 patients by 6 weeks. The advantage of this splint system is the variability of its application. The splint can be used both for nonsurgical and surgical management. It can be removed to change dressings and for radiologic evaluations. The period of dynamic treatment can be determined individually in each case. (J Hand Surg 1999;24A:1254–1262. Copyright © 1999 by the American Society for Surgery of the Hand.)