A 66-year-old male was referred to our hospital because of severe pitting edema in the lower extremities in April 2003. He had undergone a partial gastrectomy for gastric cancer 17 years before and radiotherapy for oropharyngeal cancer 1 year before. He had suffered from the edema for 4 years. Loop diuretics prescribed by his family doctor were effective for relieving the edema at first, but the edema was not resolved. He was hospitalized with evidence of hypothyroidism from blood analysis. Administration of levothyroxin partially relieved the edema, but loop diuretics were continued because the edema was not completely diminished. He was admitted to our hospital again in October 2003, because of unsteady gait and worsened edema. Neurological examination revealed the stocking-and-glove pattern of sensory disturbance and distal muscle weakness in the lower extremities. Plasma vitamin B1 (thiamine)concentration was low, and the diagnosis was beriberi. After vitamin B, supplementation was initiated, the patient's edema completely disappeared in a few days, and his gait disturbance gradually subsided. Diuretics lead to increased urinary vitamin B1 excretion, so we should be watchful for thiamine deficiency in patients treated with diuretics who underwent gastrectomy and potentially have latent vitamin B1 deficiency.