BACKGROUND: Although there is consensus that closed tendinous mallet finger injuries should be treated conservatively, the best method of immobilization to be used is not clear and the existing data in the literature are not conclusive. The aim of this study is to compare the results of four different immobilization methods used in the conservative treatment of tendinous mallet finger injury. METHODS: Ninety-six patients with tendinous mallet finger injury were treated with four different immobilization methods (stack orthosis, thermoplastic orthosis, aluminum orthosis, and Kirschner wire [K-wire] immobilization). The patients then were assessed with distal interphalangeal joint extensor lag, total active motion (TAM), grip strength, and Abouna and Brown Criteria. RESULTS: No significant difference was found between four immobilization methods in extensor lag and TAM at the 8th and 12th weeks. According to grip strength assessment, stack orthosis group was found to have significantly better results than the K-wire and aluminum orthosis groups at 12 weeks, while the difference was not significant versus the thermoplastic orthosis group. CONCLUSION: In this first study making multiple comparisons between four immobilization methods used in the treatment of tendinous mallet finger injury, the only significant difference detected between the groups was the superior grip strength with stack orthosis compared with K-wire immobilization and aluminum orthosis.