Measurement of the mammographic skin thickness over different parts of the breast was performed in 150 normal patients. The patients were divided into three groups based on breast size and the skin thickness in these three groups compared. The results showed that skin thickness decreased with increasing breast size and that the upper limit of normal was greater than the previously quoted normal range at 3.0 mm. Measurement over different parts of the breast showed that medial exceeded lateral skin thickness by up to 100%, and similarly for the inferior and superior measurements. These findings in the normal breast are of importance in deciding on the presence or absence of abnormal skin thickening as an indicator of underlying breast disease.