ObjectiveTo analyze the prevalence and severity of the opioid-induced bowel dysfunction (OBD) symptoms. DesignEpidemiological, observational and cross-sectional study. LocationSix Spanish centers participated. ParticipantsA total of 317 outpatients with a diagnosis of cancer pain or non-cancer pain treated with a unique opioid were recruited. Main measurementsThe prevalence of OBD symptoms was measured using a visual analog scale (VAS: 0-100), and constipation was also assessed by the Bowel Function Index (BFI). The treatment for gastrointestinal symptoms was recorded, and the frequency of symptoms between different opioid treatments was compared. Finally, quality of life was evaluated. ResultsThe prevalence of OBD with at least one gastrointestinal disorder was 94.6%, with constipation being the most frequent symptom (BFI: 91.6%; VAS: 90.2%) and nearly half of the patients showed three or more symptoms with a VAS ≥ 4. No significant differences were detected in the prevalence of symptoms between the opioid groups. A decrease in the wellbeing of patients was detected related to moderate to severe gastrointestinal symptoms. ConclusionsA high rate of gastrointestinal disorders probably related to OBD have been confirmed in patients on opioid therapy, highlighting the need for new drug strategies.