OBJECTIVES: The aim of this study was to establish baseline, pre-progression and post-progression health state utilities for nivolumab (NIVO) and dacarbazine (DTIC) for use in the economic evaluation of NIVO versus other interventions in unresectable stage 3 or stage 4 melanoma. METHODS: Utility data were collected during a phase III clinical trial study every 6 weeks via the EQ-5D-3L instrument and questionnaires scored using Australian specific weights within Microsoft Excel.  Utility valuations and associated patient and disease data were exported to STATA 11.2.  Descriptive statistics were generated, stratified by treatment, study epoch (screening; non-screening) and by progressive disease status. RESULTS: Two hundred and one and 208 patients were randomized to NIVO and DTIC respectively.  Mean utilities for NIVO and DTIC respectively were: 0.78 (95% CI: 0.75,0.81) and 0.71 (95% CI: 0.67,0.75) at baseline; 0.84 (95% CI: 0.83,0.85) and 0.78 (95% CI: 0.76,0.81) prior to the development of progressive disease; and 0.83 (95% CI: 0.80,0.86) and 0.70 (95% CI: 0.66,0.74) following development of progressive disease.  For those randomised to NIVO, development of progressive disease per RECIST v1.1 criteria did not significantly impact on utility (mean change=0.01, p=0.4618).  By contrast, for those randomised to DTIC, development of progressive disease per RECIST v1.1 criteria did significantly impact utility (mean change=0.08, p=0.0005). CONCLUSIONS: These results provide Australian specific utility valuations by health state to inform the economic evaluation of NIVO versus other interventions in unresectable stage 3 or stage 4 melanoma.  Notably, for those receiving NIVO, the development of progressive disease per RECIST v1.1 criteria did not have a significant impact on mean utility, suggesting the benefits of NIVO on HRQoL persist beyond traditional measures of disease progression, in contrast to DTIC which exhibits the expected reduction in utility following development of progressive disease