A fully automated approach is presented to extract brain areas efficiently from FDG-PET head scans. A threshold value is automatically calculated from the histogram graph of the brain images, followed by region growing and morphological operations, to segment brain areas from these images. Next, the midsagittal lines on axial slices are detected to separate the brain into two hemispheres. The proposed approach has been applied to 226 cases of normal controls and patients with neurological diseases. The average processing time is about 3 seconds on a standard personal computer. The experiment has shown promising results.