The paper proposes a novel active forearm orthosis, which allows the rotation motion of the elbow and the roll motion of the radioulnar joint, used as rehabilitation device in medical robotics for the humero-ulna-radial and ulna-radial joints. The theoretical part of the study consists in structural, kinematic-positional and kinetostatic analysis respectively the optimal synthesis. For the optimal design a CAD model was developed and a prototype manufactured. Many components of the prototype were manufactured by 3D printing, and it was equipped with several sensors for experimental testing. The experimental tests have recorded the angular positions of the elbow and the wrist joint, through the potentiometers and the resistant moment through current sensors on actuators. The experimental results were discussed and interpreted to confirm the theoretical studies.