Electrohydrostatic Actuation Systems (EAS) are characterized by an Electrohydrostatic Pump Unit (EPU) that directly drives a hydraulic actuator. This motion concept combines both advantages of traditional electro-mechanical actuation and electro-hydraulic actuation like high energy efficiency, environmental cleanliness, low noise emission, high force output, and no backslash. In modern IoT/I4.0 environments, the utilization of digital data plays a more and more important role such as histories of sensor data, of working cycles, or of the machine health status. In the example of an EAS, a way is shown to monitor the health status of the integrated hydrostatic machine along with the hydraulic part of such an EAS. The approach described in this paper uses the already existing sensors in an EAS, so no additional hardware is necessary. Based on a model describing the volumetric behaviour of the hydrostatic machine a volumetric health index is developed by introducing a re-normalized efficiency. The proposed methodology is independent on the overall working cycle and is therefore applicable to already running systems or systems with varying working cycle. The calculated Health Index offers the opportunity to monitor the hydrostatic machine as the key element of such an EAS in real time and in a non-invasive and continuous way.