A dialysis machine (1) includes dialysis equipment (4), a control unit (2) controlling normal operation of the machine and a safety unit (3) for monitoring the machine with a view to the problem of patient safety. The control unit controls actuators (6) and receives information from its own sensors (13). The safety unit is connected to the control unit and receives from it parameters relevant to safety which have been measured by the sensors (13) of the control unit and its own sensors (15) to receive values of the parameters and other parameters. If any abnormality is found in the parameters measured, the safety unit sends commands (SSR) relating to safe states which have to be established to the control unit (2) which controls the actuators (6) in a corresponding way. The condition of the actuators is monitored by the safety unit (3) which uses suitable sensors (17) to determine whether the actuators have carried out the required actions, and if not, Switches off the machine with its own actuators (8).