Helicobacter pylori (H. pylori) is the etiological factor for gastritis in more than half of the worldwide population. H. pylori infection increases the risk for gastric pathology, but could also have consequences on cardio-metabolic status. Obesity has as epidemic growth, and the only efficient long-term treatment for morbidly obese patients is currently surgery. Although of vital importance, the preoperative assessment is not standardized, including the aspects related to H. pylori infection. The aim of this prospective study was to evaluate the prevalence of H. pylori (Hp) infection in a group of patients referred to bariatric surgery and the agreement of two commonly used methods for its diagnosis. We included 70 asymptomatic obese patients consecutively for 14 months, who were evaluated by serology (anti-Hp IgG antibodies) and by histology (gastroscopy with gastric mucosa biopsy). If diagnosed, H. pylori infection was standard treated and afterwards, all patients underwent laparoscopic sleeve gastrectomy; the resected stomach was morphologically evaluated. 58.6% of patients were H. pylori positive on serology and 51.4% were H. pylori positive on histology, agreement coefficient factor kappa between the two methods being 0.686, p<0.001. The serological diagnosis had a sensibility of 90.3% and a specificity of 77.8%. The prevalence of H. pylori infection in the resected stomach was 11.4%, and was associated with more severe degrees of chronic gastritis. In conclusion, as gastroscopy should anyhow be performed in all patients referred to surgery, our data favor the histological evaluation in all patients and the eradication treatment according to its results.