We evaluated the outcome in 16 patients with Lambert-Eaton myasthenic syndrome (LEMS) associated with histologically verified small-cell carcinoma (SCC). Thirteen patients received specific tumor therapy (chemotherapy, radiation therapy, or resection) and most also received pharmacologic and immunologic treatment for LEMS. Seven of 11 patients surviving for more than 2 months after tumor therapy showed substantial neurologic improvement (1 patient being in complete remission at 7 years); in 3 of 11 improvement was transient. An EMG index of disease severity (compound muscle action potential amplitude in abductor digiti minimi) was significantly increased at final follow-up (p less than 0.01; n = 11). A pretreatment amplitude greater than 3.0 mV was a good prognostic sign. We conclude that a combined treatment approach in SCC-LEMS usually results in neurologic improvement.