From mid-July through late September 1970, 221 persons developed an illness characterized by acute gastroenteritis, myalgias, and lethargy. Encephalopathy became evident in 18 patients. The latter was relapsing and had a slow convalescence. Physical findings were few, and laboratory examinations were not helpful in establishing a diagnosis. This epidemic appears to be a variant of so-called "epidemic neuromyasthenia," which may be more common than medical literature would indicate.