Breast compression during X-ray mammography results in improved image quality at a lower radiation dose to the patient, and, as a consequence, the Department of Health recommends that automatic breast compression devices are fitted to mammographic X-ray units. However, the degree of breast compression is not standardized and can vary depending on the size of the patient, the particular mammography X-ray unit and the conditions of its use. A pressure measuring system was used to determine accurately the pressure on the breast. This system takes the form of a fluid-filled neonatal cuff connected to a pressure transducer by a fluid line. The pressure measuring system was calibrated and tested, first without and then with the patients, to assess its practical feasibility. The elements of the pressure measuring system, the techniques involved in its calibration and its use on patients in the clinical environment are described here. The system has proved to be a quick and simple method of relating the pressure on the breast to the pressure reading of the mammography X-ray unit.