A 78-year-old female presented with dislocation of a dual mobility hip prosthesis. On standard radiographs after closed reduction, the hip prosthesis appeared to be properly reduced, but clinically the hip was unstable. A Computed Tomography showed a round foreign body, that was in fact a dislocation of the intra-prosthetic implant. This was confirmed intra-operatively during revision surgery. Intra-prosthetic dislocation is a specific complication of dual mobility system. Classically, it's a late complication, linked to the wear of retention area of the polyethylene insert. In this case report we describe an unusual reason of intra-prosthetic dislocation caused by a reduction maneuver of a dislocated dual mobility total hip prosthesis, which to our knowledge has never been documented with Computed Tomography imagery and intra operative pictures. The aim of this article is to analyse the advantages and complications of this implant and to establish recommendations. Dealing with an intra-prosthetic dislocation of a dual mobility hip prosthesis, we recommend attempting a reduction under general anesthesia to avoid mechanical complications. In case of persistent instability after reduction, we recommend performing a Computed Tomography scan.