In recurrent glioblastoma, health-related quality of life (HRQL) is a crucial trial endpoint. We examined HRQL outcomes as a secondary endpoint for patients in the CABARET randomized phase 2 trial. 122 patients were randomly allocated to bevacizumab monotherapy or bevacizumab plus carboplatin. We calculated change scores from baseline for each HRQL measure on the European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire Core 30 (EORTC QLQ-C30) and the Brain Cancer Module (QLQ-BN20), together with time to deterioration in HRQL, and the proportion of participants with clinically meaningful improvements in specific disease-related symptoms. At baseline, 117 of 122 randomized patients (96%) attempted questionnaires. Questionnaire participation rates were >90% for patients continuing on treatment, however at the end-of-treatment visit only 72 (64% of eligible participants) returned a form. There were no differences between arms in change scores over the treatment period. Time to ≥10 point deterioration in scores from baseline was also similar between arms. HRQL deterioration occurred largely before progression for the domains tested, but scores in HRQL domains specifically relevant to symptoms of recurrent glioblastoma also improved for about 50% of patients with symptoms at baseline. Neither detrimental nor beneficial effects on HRQL were seen with carboplatin added to bevacizumab, with a proportion of patients on both arms experiencing symptomatic benefit. Given the reduced questionnaire completion at end of treatment, time to HRQL deterioration is a feasible and robust clinical trial endpoint in this patient population. Clinical trials registration number: ACTRN12610000915055.