Observed variation in hospital costs may be attributable to differences in patients' health outcomes. Previous studies have resorted to inherently incomplete outcome measures such as mortality or re-admission rates to assess this claim. This study makes use of a novel dataset of routinely collected patient-reported outcome measures (PROMs) linked to inpatient records to (i) access the degree to which cost variation is associated with variation in patients' health gain and (ii) explore how far judgement about hospital cost performance changes when health outcomes are accounted for. We use multilevel modelling to address the clustering of patients in providers and isolate unexplained cost variation. We find some evidence of a U-shaped relationship between risk-adjusted costs and outcomes for hip replacement surgery. For three other procedures (knee replacement, varicose vein and groin hernia surgery), the estimated relationship is sensitive to the choice of PROM instrument. We do not observe substantial changes in cost performance estimates when outcomes are explicitly accounted for. Copyright © 2012 John Wiley & Sons, Ltd.