Abstract Many medical disciplines initiate the evaluation of and manage the dermatomyositis-polymyositis disease complex (DM/PM). The role of the general neurologist most often is that of consultant evaluating the indolent or atypical case of DM/PM. In this instance DM/PM must be sorted out from a variety of other conditions with which it can be confused (Table 5-1), especially when skin manifestations are not present or inconclusive. In addition, neurologists often perform the electrophysiologic assessment of patients suspected of having DM/PM. Proper interpretation of the electromyogram (EMG) report can be crucial in confirming the diagnosis and committing the patient to immunosuppressive therapy. Despite its rarity in general neurological practice, DM/PM is a common condition in neurologic clinics specializing in muscle disease, and the neurologic literature is a rich repository of clinical and investigative reports on DM/PM. Increasingly, these muscle disease clinics include physicians with backgrounds in different specialties, underscoring the benefits of interdisciplinary efforts, as is illustrated in this Festschrift. This chapter will present an overview of some of the complexities of the differential diagnosis of the DM/PM from the neurological perspective, emphasizing the adult form of the disease. A review of the electrophysiologic features of this disorder will be presented and as much as is possible an attempt will be made to relate these to the evolution of the histopathologic changes. The chapter will not address etiologic or therapeutic aspects which are covered in other chapters.