We studied whether a difference exists in the development of symptoms of the Lambert-Eaton myasthenic syndrome (LEMS) between patients with or without small cell lung cancer (SCLC). We assessed symptoms in 38 LEMS patients, 13 with SCLC, by interviewing them using a structured checklist, backed up by a review of their clinical records, and compared the frequency and time scale of symptoms during the course of LEMS. Bulbar (87%) and autonomic (95%) symptoms for the whole group were more common than reported in the literature. Frequencies of symptoms did not differ significantly between patients with and without SCLC, but symptoms in patients with SCLC appeared within a shorter time-frame, indicating a more rapid clinical course. The presence of a particular symptom associated with LEMS did not predict the presence of SCLC, but in patients with rapidly progressive LEMS the possibility of underlying lung cancer should be of particular concern.