An electrically-powered device intended for 24-hour recording of the tumescence (tendency to swell) of the penis. The patient is connected to and wears the device while he performs normal daily activities and is used to register the plethysmographic measurement or function of the penile erection, e.g., length, circumference, duration of the erection. The measurements are made by, e.g., a plethysmographic sleeve or a transducer placed on the penis and the data is recorded by this device and later used by the physician for the diagnosis of penile dysfunction, e.g., impotence.