Intravenous (IV) drug abuse is known to cause pulmonary tale granulomatosis. Reports have documented a syndrome of pulmonary vascular sclerosis in long-term IV methylphenidate users. Although this would be expected to produce restrictive lung disease, we hereby report six patients who have severe obstructive lung disease. All had used IV methylphenidate for at least four years. One of these patients died of progressive respiratory insufficiency and the others are clinically disabled. Their symptoms and airflow obstruction are more severe than those of most patients with chronic obstructive pulmonary disease. In these individuals, we cannot say that precocious obstructive lung disease is not due to a combination of smoking and other factors, nor can we be certain that methylphenidate is the offending agent. However, this cluster of cases among methylphenidate abusers suggests that long-term IV exposure to this drug might lead to early severe obstructive lung disease.