The adverse effects of theophylline were recognized soon after its introduction into clinical medicine. Reports of major toxic reactions to theophylline, particularly in children, discouraged its use and led to homeopathic dosing recommendations that had little therapeutic effect. Concomitant with the renaissance in theophylline use during the past decade, reports of theophylline toxicity have increased. The epidemiology of theophylline intoxication has changed in recent years, and today most instances of serious toxicity are due to intentional overdosage, as in a suicide attempt. The adverse effects of theophylline involve the gastrointestinal, nervous, cardiovascular, and urinary systems. In addition, significant metabolic derangements are noted in patients with severe intoxication. Treatment of theophylline intoxication involves attention to fluid and electrolyte balance and initiation of measures to remove theophylline from the body (gastric lavage or emesis, repeated charcoal administration by mouth, and charcoal hemoperfusion in serious cases).