We report a case of genetically confirmed myotonic dystrophy type 2 with findings of significant inflammation in muscle. The initial presentation consisted of cramps and slowly progressive proximal muscle weakness, initially without distinguishing clinical features. Muscle biopsy showed invasion of both necrotic and nonnecrotic muscle fibers by CD4+ and CD8+ lymphocytes and upregulation of major histocompatibility complex (MHC) class I expression. Empiric immunosuppressive therapy did not provide clinical benefit. We note that several hereditary muscle disorders exhibit evidence of inflammation near necrotic fibers, believed to represent a secondary immune response. However, invasion of nonnecrotic fibers by inflammatory cells, a finding regarded as typical of primary inflammatory myopathies, has not been described in patients with myotonic dystrophy type 2. This case documents a significant inflammatory response in muscle of a patient with myotonic dystrophy type 2, which could lead to diagnostic confusion with the primary inflammatory myopathies.