The Bowel Function Index (BFI) is a clinician-administered, patient-reported, 3-item questionnaire to evaluate opioid-induced constipation in cancer and non-cancer chronic pain patients. The objective of the present analysis was to evaluate the psychometric characteristics of the BFI using data from clinical studies of oral prolonged release (PR) oxycodone/naloxone. OXN2401 was a multicenter, controlled, randomized, double-blind, parallel-group study including oral PR oxycodone combined with oral PR naloxone as well as oral PR oxycodone combined with corresponding naloxone placebo. OXN3401 and OXN3001 were 12-week multicenter, controlled, randomized, double-blind, parallel-group studies of a fixed combination of oral PR oxycodone/naloxone versus PR oxycodone. In addition, a placebo group was included in study OXN3401. BFI psychometric characteristics (reliability, reproducibility, convergent/known groups validity, and responsiveness) were evaluated. Demographic data (n=985) were comparable and analyses indicated a high degree of internal consistency (Cronbach's alpha >0.7). Change of less than 5 points in BFI was indicative of high reproducibility. Correlations between BFI item and total scores to stool frequency were statistically significant and in the low-to-moderate range (OXN2401 -0.23 to -0.29, p < 0.001; OXN3401 range -0.26 to -0.40, p < 0.001; OXN3001 -0.14 to -0.15, p < 0.05). Data indicate that a BFI score change of ≥12 points represents a clinically meaningful change in constipation. This publication for validation of BFI only includes data from three clinical trials. However, another publication of an additional specifically designed cross-sectional validation study is in preparation. The BFI is a valid and reliable instrument for the assessment of opioid-induced constipation in chronic pain patients. Psychometric analyses from clinical trials support the BFI's psychometric properties.