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A patient presented with agraphia and acalculia associated with a left frontal (F1, F2) infarction. He made mainly phonological but also lexical errors in writing (syllabograms), but his ability to write kanji (morphograms) was relatively preserved. Although he could add and subtract numbers, he could neither multiply nor divide them because of a difficulty in retrieving the multiplication tables and calculation procedures. Positron emission tomography showed decreased cerebral blood flow and metabolism limited to the infarct site. These findings suggest that agraphia and acalculia may occur associated with a left prefrontal lesion, and that the retrieval of arithmetic processes is modality specific.