Medical connection system comprising in combination: - a first coupling defining a passage coaxial with a longitudinal axis, comprising a first threaded end, - a casing, coaxial with the longitudinal axis, adapted to house at least partially the first coupling, such that the first coupling is rotatable about the longitudinal axis in the casing, and - a second coupling, defining a passage coaxial with the first coupling and comprising a second threaded end, said second coupling being adapted to be housed in the casing, the first coupling and the second coupling being rotatable in relation to one another about the longitudinal axis in the casing the system being characterised in that: - the casing further comprises means for retaining the first coupling in translation, capable of limiting the relative movement of the first coupling with respect to the casing along the longitudinal axis, means for locking in rotation the first coupling about the longitudinal axis only in the screwing direction of the first threaded end of the first coupling and means for locking in rotation the second coupling about the longitudinal axis only in the screwing direction of the second threaded end of the second coupling, the screwing direction of the first threaded end of the first coupling being opposite the screwing direction of the second threaded end of the second coupling - the second coupling is attached to the first coupling so as to lock the first coupling in translation with respect to the casing and - the first coupling comprises a first connection end and the second coupling comprises a second connection end, the first connection end being connected using latching means (14, 23) to the second connection end such that the first coupling remains rotatable about the longitudinal axis with respect to the second coupling. - a first coupling defining a passage coaxial with a longitudinal axis, comprising a first threaded end, - a casing, coaxial with the longitudinal axis, adapted to house at least partially the first coupling, such that the first coupling is rotatable about the longitudinal axis in the casing, and - a second coupling, defining a passage coaxial with the first coupling and comprising a second threaded end, said second coupling being adapted to be housed in the casing, the first coupling and the second coupling being rotatable in relation to one another about the longitudinal axis in the casing - the casing further comprises means for retaining the first coupling in translation, capable of limiting the relative movement of the first coupling with respect to the casing along the longitudinal axis, means for locking in rotation the first coupling about the longitudinal axis only in the screwing direction of the first threaded end of the first coupling and means for locking in rotation the second coupling about the longitudinal axis only in the screwing direction of the second threaded end of the second coupling, the screwing direction of the first threaded end of the first coupling being opposite the screwing direction of the second threaded end of the second coupling - the second coupling is attached to the first coupling so as to lock the first coupling in translation with respect to the casing and - the first coupling comprises a first connection end and the second coupling comprises a second connection end, the first connection end being connected using latching means (14, 23) to the second connection end such that the first coupling remains rotatable about the longitudinal axis with respect to the second coupling.