€OBJECTIVES: Chronic pain is gaining importance as a major cost factor in health care. To gather information about analgesic pharmacotherapy of patients with chronic pain and perform cost estimations to guide future cost-effectiveness research in the area. METHODS: Data from patients aged above 44 years suffering from any chronic condition and receiving regular analgesic pharmacotherapy (≥6 months) who attended health care facilities within the area of Badalona during 2008 were collected in a retrospective study. Morbidity profiles were defined according to treatment setting (pain unit, hospital), WHO analgesic stage (1-2 versus 3), and a raw cost model based on resource use and work absenteeism was applied. Patients attending the pain unit or the hospital were considered undertreated if they were on stage 1-2 analgesics. Multiple regression was used to compare costs between undertreated and non-undertreated patients among those attending the pain unit or the hospital. RESULTS: Just 410 out of 18,157 patients ascertained (2.3%) were on stage 3 analgesics. Direct health care costs were greater in patients on Step 3 analgesics (mean [SD]: 5,505.6 [5,046.4] ) than in patients on Steps 1 and/or 2 analgesics (€2,407.4 [2,436.2]), but not indirect costs (€258.5 [1,578.4] vs. €279.5 [1,423.6], respectively). Of patients attended in the pain unit and the hospital, 2.3% and 20.1%, respectively, were considered undertreated. Regression analyses revealed even greater costs in the subgroup of undertreated patients. CONCLUSIONS: Conclusion: Stage 3 analgesics are barely used. Up to one-fifth of patients may be undertreated, and prompted greater costs than those judged as properly treated. Regression analyses did not clarify what proportion of their cost excess was attributable to undertreatment.