A Latin-American teenager was begun on a regimen of acetazolamide fo a presumptive diagnosis of familial periodic paralysis. He presented 2 weeks later with near total body paralysis and was found to have florid manifestations of Graves' disease. Although thyrotoxic periodic paralysis occurs most frequently in Oriental males, it occasionally is found in Caucasians. Unlike familial, euthyroid, and periodic paralysis, thyrotoxic periodic paralysis may be worsened by administration of acetazolamide. Physical signs and laboratory evidence of hyperthyrodism must be sought in cases of periodic paralysis to differentiate the two diseases.