Although substantial progress has been made in characterizing the cognitive processes involved in simple arithmetic, the localization of these processes in the brain is not yet well understood. In this article we consider the localization of a specific arithmetic process, the retrieval of arithmetic table facts from memory. We report a single-patient study in which cortical stimulation was used to create transient disruption of brain activity in localized regions of the cortex. We show that stimulation at a left parietal site impaired performance on simple multiplication problems and further that the impairment reflected stimulation-induced disruption of arithmetic fact retrieval. Our findings support the hypothesis (e.g., Warrington, 1982) that the left parietal lobe is implicated in the arithmetic fact retrieval process.