A method for the construction of three-dimensional fibre-reinforced structures starting from a pre-existing object, wherein said method comprises the following steps: - providing a pre-existing object to which irreversibly associate three-dimensional fibre-reinforced structures, said pre-existing object being supplied without containment moulds; - acquiring an initial three-dimensional geometry of the pre-existing object and of the relative spatial coordinates of its position relative to a numerical control machine equipped with at least one printhead, disposed on an anthropomorphic robotic arm; - defining the path to be followed by said anthropomorphic robotic arm and said at least one printhead in order to add the desired amount of material to the existing object to obtain a desired final object; - feeding at least one continuous filiform element comprising at least one continuous fibre to one printhead; - laying the continuous filiform element comprising at least one continuous fibre on the pre-existing object by means of said printhead by layering the composite material on the pre-existing object according to programmed trajectories, wherein said programmed trajectories are calculated according to the path that said printhead must take to add the desired quantity of material to the pre-existing object to thereby construct said three-dimensional fibre-reinforced structures associated with the pre-existing object, said printhead moving along three mutually perpendicular axes of movement along the programmed trajectories; - subjecting said continuous filiform element to a quantity of energy such as to induce a phase change from the solid liquid state to the liquid solid state of the continuous filiform element; - extracting the final object with the three-dimensional fibre-reinforced structures, after operations are concluded. - providing a pre-existing object to which irreversibly associate three-dimensional fibre-reinforced structures, said pre-existing object being supplied without containment moulds; - acquiring an initial three-dimensional geometry of the pre-existing object and of the relative spatial coordinates of its position relative to a numerical control machine equipped with at least one printhead, disposed on an anthropomorphic robotic arm; - defining the path to be followed by said anthropomorphic robotic arm and said at least one printhead in order to add the desired amount of material to the existing object to obtain a desired final object; - feeding at least one continuous filiform element comprising at least one continuous fibre to one printhead; - laying the continuous filiform element comprising at least one continuous fibre on the pre-existing object by means of said printhead by layering the composite material on the pre-existing object according to programmed trajectories, wherein said programmed trajectories are calculated according to the path that said printhead must take to add the desired quantity of material to the pre-existing object to thereby construct said three-dimensional fibre-reinforced structures associated with the pre-existing object, said printhead moving along three mutually perpendicular axes of movement along the programmed trajectories; - subjecting said continuous filiform element to a quantity of energy such as to induce a phase change from the solid liquid state to the liquid solid state of the continuous filiform element; - extracting the final object with the three-dimensional fibre-reinforced structures, after operations are concluded.