Cerebral gliomas may cause a reduction of glucose metabolism in the cerebellum contralateral to the tumor side (crossed cerebellar diaschisis, CCD). We investigated whether CCD is related to tumor localization, histological grade, size and tumor biochemistry. Cerebellar glucose metabolism was measured in 44 glioma patients and 15 healthy subjects using positron emission tomography and [18F]fluorodeoxyglucose (FDG). CCD was determined by calculating an asymmetry index of cerebellar glucose metabolism. Further, the tumor uptake of FDG and [11C]methionine (MET) was also assessed, and was expressed as ratio of normalized tracer uptake in tumor over contralateral cortex (T/C). Frontal lobe tumors were associated with highest CCD values. For these tumors, CCD was higher in malignant (-11.8+/-9.9%) than in low-grade (-4.3+/-4.1%) gliomas (P=0.010). In addition, frontal lobe tumors showed increasing CCD values with increasing size. In tumors of the parietal or temporal lobe, CCD was less marked or absent. T/C ratios of tumor tracer uptake were higher in malignant than in low-grade gliomas, but were not correlated with CCD. Our data indicate that the magnitude of CCD is mainly determined by tumor localization and size, the latter being associated with tumor grade. These findings raise the question whether CCD provides a measure of expansion or progression particularly in low-grade tumors of the frontal lobe.