Abstract. Objectives. The aim of this study was to test the hypothesis that there are two different mallet injuries; specifically, tendinous ones are primarily low energy avulsion injuries whilst bony ones are primarily high-energy hyper-extension injuries. Methods. We reviewed in detail the demographics, mechanisms of injury, concomitant injuries and the radiological findings of patients presenting with bony and tendinous mallet deformities. The sizes of the bony fragments and angulation of the mallet deformities were measured on the initial radiographs using an established technique. Results. There were 62 tendinous mallet injuries (62 patients). These were mostly low energy injuries in men with a mean age of 57 years affecting primarily the middle and ring fingers. They were rarely associated with other injuries. There were 85 bony mallet injuries (83 patients). These were all high energy injuries also mostly in men with a mean age of 40 years primarily affecting the ring and little fingers. There were two double injuries and seven other concomitant injuries in the patients with bony mallet injuries. The extensor lags were a mean of 300 (range 3–590) for the tendinous injuries and 130 (range 0–380) for the bony injuries (p<0.00001). The fracture fragments were a mean of 51 (range 24–80) %; there was no correlation between fragment size and extensor lag. Conclusions. This study and review of the literature further confirm the substantial differences between tendinous and bony mallet injuries. In particular tendinous mallet injuries are avulsion injuries whilst bony mallet injuries are dorsal impaction fractures; they should be assessed and treated differently. Bony mallet injuries may be multiple and may be associated with other injuries. Low energy mallet deformities do not need radiographs