The association between thyroid disease and asthma is complex. Treatment of asthma in patients with thyroid disease is further complicated by the effects of thyroid dysfunction on drug metabolism. We report a patient with asthma whose calculated theophylline clearance was 0.156 L/kg/h during active Graves' disease which decreased to 0.042 L/kg/h after a euthyroid state was achieved. The potential mechanisms of this interaction are discussed and the effects of thyroid dysfunction on asthma and drug metabolism are reviewed.