Mallet finger is deformity of the extensor mechanism in the zone I, which is frequently encountered at surgical outpatientęs - departments. Active extension of distal phalanx is impossible. These injuries ranging from disruption of the extensor mechanism alone without skin disruption, with skin disruption to those that have articular involvement and subluxation of distal interphalangeal joint. The management of mallet finger injuries depends on injury pattern and includes splinting, closed reduction, percutaneous pinning with Kirschner wire, open reduction and internal fixation of extensor mechanism or bone abruptions. Non treated mallet deformity can result in chronic form, when specific therapy is needed. Correctly identified acute injury and immediate therapy can increase a possibility to complete restoration of full range of motion. This paper is focused on therapeutic principles and aftercare of closed, open and chronic injuries of extensor mechanism in the zone I.