A method for producing, by a metal powder injection moulding ("MIM") technique, a part to be produced consisting of at least one metal and/or at least one metal alloy including at least one inner cavity, comprising the following steps of: a) preparing a green core the shape of which corresponds to the shape of said cavity, this core consisting of a mixture of at least one powder of at least one ceramic and of a thermoplastic binder; b) optionally coating the green core with a anti-adhesive layer; and then performing step c), or step d), or step e); c) placing said green core optionally coated with a anti-adhesive layer, into an injection mould replicating the external shape of the part to be produced; injecting a heated liquid mixture of at least one powder of at least one metal and/or at least one metal alloy constituting the part to be produced and of a thermoplastic binder, into said injection mould around the green core, and cooling said mixture to solidify it, whereby a green part consisting of said solid mixture and comprising an inner cavity filled with the green core is obtained; d) coating said green core optionally coated with a anti-adhesive layer, with a heated liquid mixture of at least one powder of at least one metal and/or of at least one metal alloy constituting the part to be produced and of a thermoplastic binder; cooling said mixture to solidify it; and machining said mixture so that its external shape is the external shape of the part to be produced, whereby a green part consisting of said solid mixture and comprising at least one inner cavity filled with the green core is obtained; e) placing said green core optionally coated with a anti-adhesive layer between at least two green parts consisting of said solid mixture of at least one powder of at least one metal and/or at least one metal alloy constituting the part to be produced and of a thermoplastic binder; at the end of step c), or step d), or step e), successively carrying out following steps f), g), and h): f) simultaneously removing the thermoplastic binder from the green core and from the green part or from the green parts, whereby a core called a "brown" core and a part called a "brown" part or parts called "brown" parts are obtained; g) simultaneously sintering the brown core and the brown part to densify them, or simultaneously sintering the brown core and said at least two brown parts to densify them and so that said at least two brown parts are assembled together through diffusion welding around the brown core; h) removing the core, by chemical dissolution, etching, or by shakeout, whereby the part to be produced is obtained. a) preparing a green core the shape of which corresponds to the shape of said cavity, this core consisting of a mixture of at least one powder of at least one ceramic and of a thermoplastic binder; b) optionally coating the green core with a anti-adhesive layer; and then performing step c), or step d), or step e); c) placing said green core optionally coated with a anti-adhesive layer, into an injection mould replicating the external shape of the part to be produced; injecting a heated liquid mixture of at least one powder of at least one metal and/or at least one metal alloy constituting the part to be produced and of a thermoplastic binder, into said injection mould around the green core, and cooling said mixture to solidify it, whereby a green part consisting of said solid mixture and comprising an inner cavity filled with the green core is obtained; d) coating said green core optionally coated with a anti-adhesive layer, with a heated liquid mixture of at least one powder of at least one metal and/or of at least one metal alloy constituting the part to be produced and of a thermoplastic binder; cooling said mixture to solidify it; and machining said mixture so that its external shape is the external shape of the part to be produced, whereby a green part consisting of said solid mixture and comprising at least one inner cavity filled with the green core is obtained; e) placing said green core optionally coated with a anti-adhesive layer between at least two green parts consisting of said solid mixture of at least one powder of at least one metal and/or at least one metal alloy constituting the part to be produced and of a thermoplastic binder; at the end of step c), or step d), or step e), successively carrying out following steps f), g), and h): f) simultaneously removing the thermoplastic binder from the green core and from the green part or from the green parts, whereby a core called a "brown" core and a part called a "brown" part or parts called "brown" parts are obtained; g) simultaneously sintering the brown core and the brown part to densify them, or simultaneously sintering the brown core and said at least two brown parts to densify them and so that said at least two brown parts are assembled together through diffusion welding around the brown core; h) removing the core, by chemical dissolution, etching, or by shakeout, whereby the part to be produced is obtained.