A monolateral actuation system of a hip articulation, configured to be connected to an orthosis, which system comprises: - motor means, adapted to provide an assistive torque at a motor axis and configured to be arranged at a rear portion of the orthosis corresponding to the user's back; - a transmission device, connected to said motor axis for transferring said torque onto an output axis corresponding to an axis of flexion-extension of the hip and parallel to said motor axis, wherein said transmission device is configured to be arranged, in use, at a side of the user; - a fixed frame for connection to the orthosis, onto which said motor means and said transmission device are mounted; - at least one rotary joint, corresponding to a degree of freedom of abduction/adduction of the hip about a respective adduction/abduction axis, which rotary joint is interposed between said frame and said motor means, characterized in that: - the transmission device has an adjustable extension corresponding, in use, to a transverse extension in the sagittal plane of the user, said transmission device being configured to allow adjustment of a transverse distance, in the sagittal plane of the user, between said driving axis and said output axis, and the system further comprising - a linear joint, interposed between said fixed frame and said rotary joint of hip adduction/abduction, which linear joint is configured to adjust the horizontal width of the actuation system on the frontal plane of the user, the overall configuration being such that said motor means and said transmission device are floating with respect to said frame. - motor means, adapted to provide an assistive torque at a motor axis and configured to be arranged at a rear portion of the orthosis corresponding to the user's back; - a transmission device, connected to said motor axis for transferring said torque onto an output axis corresponding to an axis of flexion-extension of the hip and parallel to said motor axis, wherein said transmission device is configured to be arranged, in use, at a side of the user; - a fixed frame for connection to the orthosis, onto which said motor means and said transmission device are mounted; - at least one rotary joint, corresponding to a degree of freedom of abduction/adduction of the hip about a respective adduction/abduction axis, which rotary joint is interposed between said frame and said motor means, characterized in that: - the transmission device has an adjustable extension corresponding, in use, to a transverse extension in the sagittal plane of the user, said transmission device being configured to allow adjustment of a transverse distance, in the sagittal plane of the user, between said driving axis and said output axis, and the system further comprising - the transmission device has an adjustable extension corresponding, in use, to a transverse extension in the sagittal plane of the user, said transmission device being configured to allow adjustment of a transverse distance, in the sagittal plane of the user, between said driving axis and said output axis, and the system further comprising - a linear joint, interposed between said fixed frame and said rotary joint of hip adduction/abduction, which linear joint is configured to adjust the horizontal width of the actuation system on the frontal plane of the user,