Proton magnetic resonance spectroscopy (1HMRS) provides biochemical information from tissue non-invasively, and has an evolving role in brain tumour diagnosis and management. We present 100 consecutive patients with brain tumours who had single voxel 1HMRS as part of their preoperative investigations. We report the histopathological findings and the diagnostic contribution of spectroscopy in an adjunctive role. On the basis of clinical and radiological information the preoperative diagnosis was unclear or inaccurate in 26 out of 100 cases. The discrepancy was of lesion grade in 17 cases and lesion type in 9 cases. In 6 of 100 patients with brain tumours 1HMRS could have made a significant contribution to the preoperative diagnosis if used as part of the routine assessment. There is therefore a useful role for 1HMRS in the evaluation of intracranial mass lesions.