In order to evaluate the role of proton MR spectroscopy (1H-MRS) in the diagnosis and assessment of long-term radiation-related neurotoxicity, 14 children who had received cranial irradiation for the treatment of childhood leukaemia (n = 6) or brain tumours (n = 8) underwent 1H-MRS, MRI and neuropsychological assessment. Short-term effects at 2 months following treatment were studied in a further three patients. MRI abnormalities were observed in nine patients. No statistically significant differences between patients and controls (n = 17) were seen in any of the calculated 1H-MRS metabolite ratios, in any of the three patient groups. On multivariate logistic regression analysis there was a correlation between the choline/water ratio and a low IQ. It is concluded that any systematic radiation-induced changes in the 1H MRS metabolites must be below the detection threshold of this study.