The long-established observation that some rheumatologic disorders (RDs) are associated with--or precede--the clinical manifestations of a variety of solid and hematological tumors represents an important clue for the early diagnosis and effective treatment of the cancers. Inflammatory myopathies, seronegative rheumatoid arthritis and some atypical vasculitides are the most frequently reported paraneoplastic RDs, although paraneoplastic scleroderma- and lupus-like syndromes, erythema nodosum, and Raynaud's syndrome have also been observed. Generally, the clinical course of a paraneoplastic RD parallels that of the cancer, and surgical removal of the tumor or its medical treatment usually results in a marked regression of the clinical manifestations of the RD. Most paraneoplastic RDs are difficultly distinguishable from idiopathic RDs. Even so, some atypical features of the clinical presentation raise the suspicion of an underlying tumor. This review summarizes current hypotheses for the pathogenesis that leads a tumor to present as an RD and discusses the clinical features that help distinguish paraneoplastic from idiopathic RDs.