Forty morbidly obese asthmatic patients who underwent gastric restrictive surgery more than 2 years earlier were evaluated to determine the influence of weight loss on asthma outcome. Mean percentage excess weight loss in this group was 68% and body mass index (BMI) fell from a mean of 46 to 30. Following surgery, 90% showed improvement in asthma symptoms. Complete remission of asthma occurred in 48% and a further 12.5% became asthma free on reduced medications dosage. Of those taking daily medications for asthma before surgery, 42% were completely off medication following weight loss surgery, and another 18.5% experienced fewer asthma attacks on reduced medication dosage. Of the 22 patients with severe asthma (> 10 attacks per year) on routine daily medications for asthma preoperatively, 8(36%) required no medication after surgery, 7(32%) used medication only on an 'as-needed' basis, and 7(32%) controlled their asthma on reduced medication dosage. Five patients gained weight during the follow-up period. All developed an increased incidence of asthma attacks, which again abated after successfully losing weight following revisional surgery. Coexistent factors of smoking and clinically apparent esophageal reflux were evaluated, but no statistically significant correlation was shown with either smoking or reflux and improvement in asthma. Possible etiologies of the improvement in asthma with weight loss are discussed