Recent models of lexical processing suggest that written spelling partly depends upon the semantic system. According to these models, a deterioration in word meanings would necessarily lead to a spelling impairment, especially for low-frequency and orthographically irregular words. We report a case study of a patient (MK) with semantic dementia who presents impairments in knowledge of word meanings and surface dysgraphia. By specifically identifying concepts that are still known or that are partially or completely deteriorated, we show that the patient's spelling deficit is highly correlated with word comprehension. These data confirm that surface dysgraphia is directly linked to the breakdown in semantic memory.