A method for the preparation of injectable ready-to-use paste bone cement compositions by mixing a dry inorganic bone cement powder comprising a particulate calcium sulfate hemihydrate capable of hardening in vivo by hydration of the calcium sulfate hemihydrate forming calcium sulfate dihydrate, an aqueous liquid and an additive that normally retards the setting process, said method comprising a) providing a bone cement powder comprising calcium sulfate hemihydrate, an accelerator for the hardening of the calcium sulfate hemihydrate by hydration, said accelerator being selected from the group consisting of saline and calcium sulfate dihydrate, and a powdered calcium phosphate component b) mixing the bone cement powder with the aqueous liquid for a period of time c) leaving the mixture for the time needed for allowing the hydration reaction of the calcium sulfate hemihydrate to proceed and allowing calcium sulfate dihydrate crystals to form and grow, and d) admixing the additive by means of a short-duration mixing using a minimum of energy surprisingly shortens the setting times for the cement comprising the addi tive that retard the setting process to the level observed in the absence of the additive and enables a complete hydration of calcium sulfate hemihydrate to calcium sulfate dihydrate, even when using additives else preventing the hardening.Linvention porte sur un procédé pour la préparation de compositions de ciment osseux en pâte prêt à lemploi injectable par le mélange dune poudre de ciment osseux inorganique sèche comprenant un sulfate de calcium semi-hydraté particulaire pouvant durcir in vivo par hydratation du sulfate de calcium semi-hydraté formant du sulfate de calcium dihydraté, un liquide aqueux et un additif qui normalement retarde le processus de prise, ledit procédé consistant à : a) utiliser une poudre de ciment osseux comprenant du sulfate de calcium semi-hydraté, un accélérateur pour le durcissement du sulfate de calcium semi-hydraté par hydr
