Thyrotoxic periodic paralysis (TPP) is characterized by recurrent episodes of muscle weakness and hypokalemia associated with thyroid hyperactivity. Reported predominantly among individuals of Asian descent, TPP is a rare manifestation of hyperthyroidism in western populations. We describe a typical case of TPP in a 33-year-old portuguese male, who presented with acute tetraparesis associated with hypokalemia (K+ 2.6 mEq/L). The patient had a 8-week history of several episodes of paraparesis of variable intensity; these attacks were usually nocturnal, preceded by strenuous exercise and resolved spontaneously after a few hours. The presence of tachycardia, weight loss, and goiter led to the diagnosis of Graves's disease. The correction of the hyperthyroid function with metimazol and propranolol prevented further episodes of muscle weakness. Thyrotoxic periodic paralysis should be considered in the differential diagnosis of acute episodes of motor paralysis in young patients. The maintenance of a euthyroid status is an essential part of management as this prevents the paralytic episodes.