From January 1, 1992, through January 14, 1994, the Ministry of Public Health of Cuba (MINSAP) identified 50,862 cases of a neuropathy in residents of Cuba (1993 population: 10.8 million); affected persons had onset beginning July 1, 1991. The neuropathy has included an optic form--characterized by subacute (i.e., 3-30 days) onset, decreased visual acuity, decreased color vision, and/or central or cecocentral scotomata--and a peripheral form; both forms have been characterized by weight loss and easy fatigability. This report presents a preliminary summary of an investigation by MINSAP of this epidemic.