This surgical instrumentation assembly for positioning an ankle prosthesis including a tibia implant (18) and a talus implant (16), comprises a talar alignment instrument (2) adapted to be placed on a talus (T) of a patient, and relative to the rotational plane (P1) of the talus, and centered on the rotational axis (X1) of the talus, and perpendicular to the rotational plane of the talus (T) and mechanically attached to the talus (T), and a cutting block (5) adapted to be fastened to the talar alignment instrument (2) and locked with respect to a tibia (B) of the patient.
