We present three cases of the adult opsoclonus-myoclonus syndrome in patients with systemic carcinoma. In addition to opsoclonus and myoclonus, other clinical components of the syndrome can include ataxia, tremor, gait and stance dysfunction, altered mental status, and head and face dyskinesias. The most common etiologies are idiopathic, paraneoplastic, and infectious encephalitis. Radiographic and pathological studies suggest brain-stem dysfunction with associated cerebellar and/or cerebellar pathway dysfunction. In many cases, there is evidence for the involvement of immunologic and/or inflammatory processes in the pathogenesis of this syndrome. The timely recognition of this syndrome is important because of its implications for the underlying etiology and prognosis. The appearance of this syndrome should prompt the search for an occult malignancy.