The present study was aimed at differentiate, within the parietal cortex, the areas underlying visuospatial working memory/attentionnal processes and those devoted to arithmetic processing. We compared, using positron emission tomography, the cerebral networks activated in two groups of subjects, one solving two-by-two digit numbers multiplications and the other performing a visuospatial non-numerical N-Back task. Both tasks were compared to a resting state and a control condition. During both tasks, activation was observed, bilaterally, in superior parietal areas reflecting visuospatial working memory and attentionnal processes shared by both tasks. The calculation task elicited more activation in the left inferior parietal lobule and the left precuneus. These areas could subtend numerical representation, numbers storage and retrieval processes. These results added some strong support for a special role of the left inferior parietal areas in arithmetic processing.