The invention relates to a device for the extemporaneous preparation of an amount of sterile treatment fluid comprising a syringe (4) for administration and a device (5, 6) for connection / sterilization by filtration. The fluid inlet (34) of the connection / sterilization device (5, 6) is incompatible with any female frustoconical tip which would be compatible with the male frustoconical tip of the syringe (4), so that the hermetic connection of said fluid inlet (34) of the device (5, 6) connection / sterilization to such a frustoconical tip female is impossible.
