Gastric partitioning has been proposed as an alternative to jejunoileal bypass for the control of morbid obesity because of the relative ease of performance and the lack of metabolic complications. From our series of 250 patients who underwent gastric partitioning, one of them developed a neurologic syndrome consistent with Wernicke's disease. The clinical findings were characterized by ataxia, confusion, impaired extra-ocular movements with diplopia, and weakness. A second patient with a similar condition was referred to us for evaluation and treatment. Pretreatment thiamine levels were normal in one case and revealed thiamine deficiency in the second. The study group of 15 patients had thiamine and red cell transketolase levels determined before, 6 wk, and 1 yr after gastric partitioning. A significant drop in values was seen at 6 wk postoperatively. Gastric partitioning is a safe and effective alternative to jejunoileal bypass in the control of morbid obesity. However, severe permanent neurologic deficits, probably related to thiamine deficiency, may occur.