The Radiation Therapy Oncology Group (RTOG) embarked on a phase I/II study of patients suffering from glioblastoma multiforme (protocol 98-03) to assess the impact of dose escalation with 3-D conformal techniques. The primary endpoints were feasibility and survival. This report describes the outcome of secondary endpoints (quality of life and neurocognitive function). Patients with supratentorial GBM were treated with a combination of carmustine (BCNU) and conformal irradiation (dose levels: 66, 72, 78, 84 Gy, respectively). Quality of Life was assessed with the Spitzer Quality of Life Index. Neurocognitive function was determined by the Mini Mental Status Examination. The latter tests were administered at the start of irradiation, at the end of irradiation and then at 4 month intervals. Relatively high compliance was achieved with both of the tools (SQLI; MMSE). Overall rates of survival between baseline SQLI scores <7 and 7-10 were statistically significantly different [HR = 1.72, 95% CI (1.22, 2.4), P = 0.0015]. The significant impact of high SQLI score on survival was preserved in multivariate analysis. The component of this index which made the greatest contribution was the patient's independence. There was continual deterioration of neurocognitive function within the populations studied. No correlation was seen between dose escalation and the secondary endpoints studied. Radiation dose escalation and assessment of its impact on life quality and neurocognition can be carried out in a large international trial. Baseline SQLI is a statistically significant determinant of survival. Those who maintain independence have superior survival to those who are reliant on others.