In this study we investigated the acalculic condition of a patient, C. G., with the classical signs of Gerstmann's Syndrome: finger agnosia; right-left disorientation; a profound agraphia (but with an equally profound alexia) and a remarkably dense acalculia. Using a series of number processing and number knowledge tasks, a selective impairment for numbers was demonstrated. Within the category of numbers C. G. showed a largely preserved ability to deal with numbers below 4, in all tasks and in all modalities, while she was totally unable to deal with numbers above 4. The consistency of responses and the ineffectiveness of cueing indicated that numbers above 4 were lost, rather than hard to access. Further testing showed that this impairment did not result from a more general semantic memory problem, a difficulty in understanding quantities or a deficit in reasoning abilities thought to underlie the concept of numbers. Difficulty with some other ordinal structures was also present, but appeared unrelated to those affecting numbers.