In a multi-centre randomised clinical trial comparing dacarbazine (DTIC) plus recombinant interferon-alfa2a (IFN) versus DTIC alone for patients with metastatic malignant melanoma, aspects of quality of life (QL) were measured prospectively by patients using linear analogue self assessment (LASA) scales including the GLQ-8 and by doctors using Spitzer's QL Index. QL scores and performance status at the time of randomisation were available for 152 of 170 eligible patients. These scores carried significant prognostic information. In univariate analyses, Spitzer QL Index assessed by the doctor and LASA scores for physical wellbeing (PWB), mood, pain, appetite, nausea and vomiting, GLQ-8 total and overall QL were significant (P < 0.01) predictors of subsequent survival. QL Index and LASA scales for mood, appetite, and overall QL remained independently significant (all P < 0.05) in multivariate models allowing for significant prognostic factors other than QL (liver metastases and performance status). These findings closely parallel those in patients with metastatic breast cancer. They add further validity to the QL Index and LASA scores, provide the first evidence of the prognostic significance of the GLQ-8, and argue strongly for the routine assessment of QL in future therapy trials.