Corrugated diaphragms are used for pressure measurement and control in a variety of applications. Their designs have become more critical in recent years because of the trend towards miniaturisation and the necessity to increase their stiffness to minimise vibration effects which demands the use of higher working stresses. This is particularly true of precision equipment used in aircraft applications. Finite element computer models were constructed and the predicted deflections compared with the measured ones to assess the accuracy of their predicted stresses. A pressure cycling rig has been designed and built enabling a series of fatigue tests to be done on diaphragms. The results were compared with the fatigue properties of the material in tension and bending, enabling a fatigue criterion, based on the tensile strain on the maximum shear plane, to be postulated. The effects of cyclic loading on diaphragms' pressure/deflection curves was also investigated. The results of the theoretical investigations and the fatigue teats have been combined to produce design criteria and graphs for the guidance of designers.