We examined cerebral activation patterns with positron emission tomography (PET) in 12 right-handed normal volunteers while they were completing simple calculation tasks or merely repeating numbers. Using a parametric experimental design, during calculation we found activation in the medial frontal/cingulate gyri, left dorsolateral prefrontal cortex, left anterior insular cortex and right anterior insular cortex/putamen, left lateral parietal cortex, and the medial thalamus. Number repetition engaged bilateral inferior sensorimotor cortex, bilateral temporal areas, and left inferior frontal cortex. These results suggest a functional anatomical network for simple calculation, which includes aspects of attention, auditory, and motor processing and the phonological store and articulatory loop components of working memory; they add some support for a special role of the parietal cortex in calculation tasks.