Background: Multiple myeloma (MM) is a plasma cell dyscrasia characterized by a clonal proliferation of plasma cells that produces a monoclonal protein. There are dermatologic disorders that have been associated with MM, such as amyloidosis, cryoglobulinemia, POEMS syndrome, normolipemic plane xanthoma, and plasmacytoma. The high volume of patients with MM seen at our institution presents an opportunity to define more extensively the spectrum of cutaneous diseases seen in concert with MM. Design: We reviewed 2357 pathology reports of all patients with a diagnosis of MM to find those who had undergone a skin biopsy. Files were searched for bone-marrow diagnosis, and for type and number of transplants. Results: In all, 284 patients yielded 472 skin biopsy specimens (average 1.7/patient). Skin biopsy specimen diagnoses included neoplastic lesions, (111; 73 malignant, 38 benign), graft-versus-host disease (120), drug-related lesions (46), cutaneous eruption of lymphocyte recovery (3), thrombocytopenia-related lesions (9), normolipemic plane xanthoma (1), amyloidosis (1), Sweet's syndrome (7), panniculitis (1), papulosquamous lesions (18), bullous diseases (17), vasculitis (11), infectious lesions (41), granulomatous dermatitis (6), alopecia cicatrisata (1), nonspecific lesions (77), and unrelated lesions (2). Conclusions: Skin biopsy specimens from patients with MM less than 60 days from transplant most commonly show sequelae of the transplant such as graft-versus-host disease, Grover's disease (as a result of leukocytopenia and fever, waiting for engraftment), drug eruptions, chemotherapy effect, thrombocytopenic effect, cutaneous eruption of lymphocyte recovery, and Sweet's syndrome (possibly as a result of granulocyte-macrophage colony-stimulating factor). Biopsy specimens taken more than 60 days from transplant most commonly show graft-versus-host disease, drug eruptions, and Sweet's syndrome but also show unrelated conditions such as neoplastic lesions, nevi, papulosquamous lesions, vasculitis, infections, and nonspecific changes. (J Am Acad Dermatol 2003;48:497-507.)