PURPOSE: To correlate the findings of gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA)-enhanced MR imaging with positron emission tomography (PET) in the evaluation of central nervous system neoplasia. MATERIALS AND METHODS: Thirty-six lesions identified on noncontrast MR in 35 patients with biopsy-proved intracranial tumors were imaged with both T1-weighted Gd-DTPA MR at 1.5 T and [18F]2-fluoro-2-deoxyglucose (FDG) positron emission tomography (PET). Eighteen women and 17 men with a mean age of 47.1 years (range 22-72) were studied. The degrees of Gd-DTPA enhancement and FDG uptake were rated separately, and then all scans were reviewed together. FDG uptake was graded 1-5. RESULTS: Of the 35 lesions rated, 30 had Gd-DTPA enhancement and 28 of these were hypermetabolic (FDG accumulation greater than white matter) on PET (93% concordance). Twenty-six of 32 neoplastic lesions had Gd-DTPA enhancement. Twenty-four of these enhancing tumors were hypermetabolic. Only one lesion was completely missed on PET but identified on routine spin echo MR. CONCLUSION: Gd-DTPA MR and FDG-PET are complementary and there is a high concordance of Gd-DTPA-enhancing tumours displaying FDG hypermetabolism. Although FDG hypermetabolism and Gd-DTPA enhancement are usually suggestive of high-grade malignancy, anaplastic astrocytomas may not enhance with Gd-DTPA and can be hypometabolic. In addition, benign intracranial tumors (two cases of meningioma) and radiation necrosis can be associated with both FDG uptake and Gd-DTPA enhancement.