BACKGROUND: vertical banded gastroplasty (VBG) and gastric bypass Roux-en-Y (GBP) are adjunctive to lifelong commitment to energy restricted diet in the attempt by the severely obese to lose weight and maintain weight loss. METHODS: the outcome of 48 subjects (36 VBG and 12 GBP) is presented. RESULTS: 18 months nutritional counseling and follow-up indicated VBG and GBP to be equally effective in maintaining appreciable weight loss. Achievement of 'functional weight', such as minimum 50% loss of excess body weight for at least 12 months Post-operatively occurred in the majority of patients. Excess weight loss by GBP and VBG was 77% and 54% respectively during the first 6 months, with 7-15% additional loss during the next 12 months. BMI decreased from an average 43 to 27 kg m(2) after 12 months. During the first 3 months, energy intake was approximately 2930 kJ, increasing to;4605 kJ at 6 months, to; 5860 kJ at 12 months and then stabilizing. Intake of;50% of the Recommended Daily Allowance (RDA) for most vitamins and minerals was reached. Hemoglobin, iron, folic acid and thiamin values were in the normal range for the entire 18 months follow-up, while serum vitamin B12 levels decreased to deficiency levels during the same period. The pre-operative moderately elevated triglycerides, cholesterol, glucose and insulin levels returned to normal range, thereby alleviating the need for medication and reducing the risk of obesity-related morbidity. Most subjects were quickly satiated with small amounts of solid foods and did not report hunger feelings for the first 6 months post-operatively. The main significant changes in food preferences in the first 6 months were the decrease in starch-based products and the increase in semi-solid milk products and eggs. CONCLUSION: taken together these observations suggest that the subjects should be strongly advised to partake in structured counseling for an extended period of time.