BACKGROUND: The long-term efficacy of laparoscopic Roux-en-Y gastric bypass (RYGB) in the treatment of morbid obesity has been demonstrated. Laparoscopic sleeve gastrectomy (SG) as a single procedure has shown promising short-term results, but the long-term efficacy of SG has not yet been demonstrated. The aim of this study was to determine the preliminary 30-day morbidity and mortality of RYGB and SG in a prospective multicenter randomized setting. METHODS: A total of 240 morbidly obese (BMI = 35-66 kg/m²) patients evaluated by a multidisciplinary team were randomized to undergo either RYGB or SG. There were 117 patients in the RYGB group and 121 in the SG group; two patients had to be excluded after randomization. Both study groups were comparable regarding age, gender, BMI, and comorbidities. RESULTS: There was no 30-day mortality. The median operating time was significantly shorter in the SG group (66 min vs. 94 min, p < 0.001). All complications were recorded thoroughly. There were 7 (5.8 %) major complications following SG and 11 (9.4 %) after RYGB (p = 0.292). Nine (7.4 %) SG patients and 20 (17.1 %) RYGB patients had minor complications (p = 0.023). The overall morbidity was 13.2 % after SG and 26.5 % after RYGB (p = 0.010). There were three (2.5 %) early reoperations after SG and four (3.3 %) after RYGB (p = 0.719). CONCLUSIONS: At 30-day analysis SG is associated with a shorter operating time and fewer early minor complications compared to RYGB. There were no significant differences in major complications or early reoperations. Long-term follow-up is required to determine the effect on weight loss, resolution of obesity-related comorbidities, and improvement of quality of life.