Hyperthyroidism may present various muscular diseases, namely thyrotoxic chronic myopathy, myasthenia gravis, disthyroid ophthalmopathy and thyrotoxic periodic paralysis. Although infrequent, it is possible to find some of these clinical situations in a medical ward of a general hospital. Differential diagnosis must be made with chronic idiopathic polymyositis and certain congenital myopathies. We describe three patients with hyperthyroidism; one of these patients had chronic thyrotoxic myopathy and another had myasthenia gravis. The third had a thymolipoma and ocular changes probably corresponding to myasthenia gravis.