Background: Clinical observation reveals a close association between morbid obesity and a variety of serious medical conditions. This report describes the changes observed in some of these co-morbid conditions, following weight loss achieved by silastic ring gastric bypass (SRGBP). Methods: Between 1990 and 1998, 157 severely obese patients aged 15-62 years underwent SRGBP. Initial and follow-up data was recorded prospectively on a computerized database, with minor subsequent additions being achieved by phone call or questionnaire. Particular attention was given to associated comorbidities and improvement in these that occurred during follow-up. Median pre-operative BMI was 45 (33-97). Patients were followed for a median 2.5 years. At 2 years post-SRGBP, median BMI was 28 (20-52). Weight loss was statistically significant (p<0.0001). Results: Before surgery 42 patients were being treated for hypertension and 34 for asthma. Withdrawal of all medication for these conditions was achieved sometime after surgery in 18 and 17 patients respectively. NIDDM was present in 19 patients before surgery and subsequently resolved completely in 18. Eleven of the 12 patients with recognized obstructive sleep apnea before surgery had resolution of this after surgery. Dyslipidemia was present in the majority of patients before surgery and resolved or improved following surgery in almost all instances. Conclusions: The findings indicate that reliable and substantial weight loss can be accomplished by gastric bypass surgery with accompanying major reductions in associated co-morbidities. Such benefits suggest that greater attention should be given to this form of treatment for those with severe obesity.