We describe a 23-year-old woman with a 3-week history of episodic leg weakness. The onset of weakness always occurred in the evening after dinner and the attacks resolved spontaneously by morning. Physical examination revealed a resting tachycardia and symmetrical, proximal weakness involving both arms and legs. Electrocardiogram (ECG) and electrolyte analysis showed a severe hypokalemia and thyroid function tests showed hyperthyroidism. The patient was diagnosed as having Graves' thyrotoxicosis and thyrotoxic periodic paralysis (TPP) and was initially treated with propranolol and subsequently carbimazole. No recurrence of the paralysis has been noted. TPP is most common in males of Asian extraction and is rare in women even in the Asian population. With increasing immigration, TPP is likely to occur more frequently in both Europe and North America and awareness of the condition is vital. Treatment of the underlying thyroid dysfunction cures the muscle symptoms.