Hydroxychloroquine causes a vacuolar myopathy that is usually of mild to moderate severity. The myopathy may be underrecognized, especially in patients who receive multiple other medications for complex illnesses. We report two patients with connective tissue diseases and unusually severe, histopathologically proven hydroxychloroquine myopathy. Both had ventilatory failure; one also had primary pulmonary disease associated with scleroderma, but the other lacked a pulmonary etiology. The ventilatory failure and subsequent medical complications led to death despite discontinuation of hydroxychloroquine, thereby underscoring the potential severity of hydroxychloroquine myopathy and the need for its early recognition.