Hypokalemic periodic paralysis is a rare life-threatening syndrome, potentially reversible when detected at an early stage. Hypokalemia may also occur in other conditions characterized by muscle weakness. Acute myopathy associated with thyrotoxicosis has been described in Asian populations, although it seldom affects Caucasians or African-Americans. It can be difficult to recognize in western populations. Acute recurrent episodes of flaccid paralysis, symmetrically affecting the proximal muscles of the lower limbs, either following strenuous physical activity or carbohydrate overindulgence, is the usual presentation. Hypokalemia seems to result from transcellular shifts of potassium rather than losses. A case of thyrotoxic hypokalemic periodic paralysis occurring in a young Caucasian male diagnosed with Graves' disease is reported.