The paper discusses the susceptibility to electromagnetic interference (EMI) of active robots for surgery, which are safety-critical systems. The high EMI environment of an operating room in the presence of an electrosurgical generator is considered. Experience of a surgeon assistant robot for prostatectomies in improving the immunity to EMI is described. It has been found that effective isolation of the robotic system hardware from grounded metal objects provides significant improvements to safety by its immunity to EMI, in minimising the flow of high-frequency current to ground through the system hardware.