Dislocations at the carpometacarpal joints are uncommon and can be overlooked due to the subtle nature of the radiographic findings. The diagnosis requires a proper understanding of the normal radiographic anatomy of the carpometacarpal joints. To aid in our understanding of the injury, anatomic dissections of the hand were performed. From these, we drew several conclusions about the mechanism of injury. Diagnostic criteria were then developed and applied in the review of a series of CMC dislocations. The incidence and diagnostic characteristics are presented. A systematic approach emphasizing the posteroanterior view and utilization of the parallel "M", principles of parallelism, symmetry, overlapping articular surfaces, and a distinct cortical rim are presented.