Patient ratings of satisfaction with their postoperative pain treatment tend to be high even in those with substantial pain. Determinants are poorly understood and have not previously been studied in large-scale, international datasets. PAIN OUT, a European Union-funded acute pain registry and research project, collects patient-reported outcome data on postoperative day 1 using the self-reported International Pain Outcome Questionnaire (IPO), and patient, clinical, and treatment characteristics. We investigated correlates of satisfaction and consistency of effects across centres and countries using multilevel regression modelling. Our sample comprised 16,868 patients (median age 55 years; 55% female) from 42 centres in 11 European countries plus Israel, USA, and Malaysia, who underwent a wide range of surgical procedures, for example, joint, limb, and digestive tract surgeries. Median satisfaction was 9 (interquartile range 7-10) on a 0-10 scale. Three IPO items showed strong associations and explained 35% of the variability present in the satisfaction variable: more pain relief received, higher allowed participation in pain treatment decisions, and no desire to have received more pain treatment. Patient factors and additional IPO items reflecting pain experience (eg, worst pain intensity), pain-related impairment, and information on pain treatment added little explanatory value, partially due to covariate correlations. Effects were highly consistent across centres and countries. We conclude that satisfaction with postoperative pain treatment is associated with the patients' actual pain experience, but more strongly with impressions of improvement and appropriateness of care. To the degree they desire, patients should be provided with information and involved in pain treatment decisions.