A comparative study between perfusion magnetic resonance (MR) imaging and single photon emission tomography - computed tomography (SPECT-CT) was performed to disclose the indications and limits of the two techniques for brain tumour characterization. We compared these two techniques because they evaluate the entire brain and often a brain tumour can be too large to be studied entirely with MR spectroscopy. Forty-three patients with 56 lesions were studied with both techniques. The sensitivity in identifying neoplastic tissue was achieved. We did not evaluate the diagnostic sensitivity to differentiate high grade from low-grade tumours because the features of grade II astrocytomas with SPECT-methoxyisobutylisonitrile (SPECT-MIBI) are similar to those of normal brain tissue. Another question that advanced diagnostic techniques can solve is real glioma extension, but we did not consider also this aspect due to the low SPECT-MIBI spatial resolution. In 29 (29/56) cases both techniques accurately identified the presence of neoplastic tissue. Only SPECT-CT was positive in eight cases, whereas perfusion MR was falsely negative. Only perfusion MR identified tumoral tissue in four cases and SPECT-CT not. Finally both perfusion MR and SPECT-CT failed to identify neoplastic tissue in 15 cases out of 56. In most cases the diagnostic gain of both techniques was the same. One technique was superior to the other in only in a few cases. We conclude that, if available, both techniques can be used to study suspected brain tumours to better characterize the lesion.