BACKGROUND: During the last 5 years, the performance of bariatric operations has doubled via our outpatient obesity clinic. Currently, 52% of the patients presenting for weight loss are interested in bariatric surgery. Gastric banding and Roux-en-Y gastric bypass are the two laparoscopic procedures proposed. The aim of this study was to evaluate the impact of preoperative teaching on the patients' surgical option. METHODS: All the candidates for bariatric surgery were submitted to preoperative teaching and those between February 2001 and December 2002 are the subject of this study. The teaching consisted of 3 weekly interactive 2-hour sessions. During the first session, the patients were asked about the type of operation that they had in mind: gastric banding, gastric bypass, or not yet decided. The same questions were repeated at the end of the third session, with an additional possible answer: no surgery. RESULTS: 297 consecutive patients with a BMI >35 kg/m(2) with at least one severe co-morbidity, were submitted to preoperative teaching. 80% of the patients were women. Median age was 41 years. Before teaching, 68 patients (23%) were uncertain, 100 (34%) favored gastric banding, and 129 (43%) wanted a gastric bypass. After education, only 3 patients (1%) remained uncertain, 45 (15%) changed their surgical option, and 27 (9%) declined surgery. The proportion of patients opting for gastric banding decreased from 34% to 20%, whereas those electing bypass increased from 43% to 70%. CONCLUSIONS: Preoperative training provides an informed and better patient selection for bariatric surgery. It helps the patients understand the various surgical options, and makes their decision easier.