Background Lactose intolerance is a frequent gastrointestinal disease affecting 47% of the Eastern European population. Small intestinal bacterial overgrowth (SIBO) leads to carbohydrate malabsorption and therefore to false results during lactose breath and tolerance tests. Objectives We aimed to assess the prevalence of lactose maldigestion and intolerance in Hungary and to investigate the role of combined diagnostic method and testing for SIBO in reducing false results. Methods We retrospectively analyzed data from 264 adult symptomatic patients who underwent 50g lactose breath and tolerance tests in parallel over a one-year period at our center. A �20 ppm elevation of H 2 or less than 1.1 mmol/l rise of blood glucose was diagnostic for lactose maldigestion. Patients with maldigestion who had symptoms during the test were defined as lactose intolerant. Patients with an early (�90 min) significant (�20 ppm) rise of H 2 during lactose and/or lactulose breath tests were determined to have SIBO. Patients with slow/rapid oro-cecal transit and inappropriate preparation before the test were excluded. Results 49.6% of the 264 patients had lactose maldigestion, and 29.5% had lactose intolerance. The most frequent symptom was bloating (22.7%), while 34.8% of the study population and 60% of the symptomatic patients had SIBO. In 9.1% and 9.8% of the patients, the lactose