Injection needle assembly having opposite distal and proximal ends, and wherein the assembly comprises: - an injection needle having proximal and distal pointed ends, wherein the distal pointed end is arranged to penetrate a membrane arranged at the proximal end of a medicament container; - a tubular needle holder partially surrounding and fixedly connected to said injection needle, wherein said needle holder comprises on its outer circumferential surface ledges on a distal area and cut-outs on a proximal area; - a tubular cap comprising a distal part having container attachment means, a proximal part having bayonet fitting grooves on its outer circumferential surface, said tubular cap further comprising a central passage having bayonet fitting grooves (36, 38) on its inner circumferential surface adapted for receiving the ledges of the needle holder; - a tubular needle cover comprising on its inner circumferential surface, first ledges arranged to cooperate with the cut-outs of the needle holder, and second ledges arranged to cooperate with the bayonet fitting grooves of the cap; characterized in that said needle cover is arranged to be displaced axially by linear displacement in a distal direction in relation to said cap with the second ledges of the needle cover along said bayonet fitting grooves of said cap, wherein said needle holder is displaced axially distally due to the engagement between the first ledges of the needle cover and the cut-outs of the needle holder, that said needle cover is arranged to then be twisted whereby said needle holder is twisted, wherein said second ledges of said needle holder engages with transversal sections of said bayonet fitting grooves of said cap, preventing proximal displacement of said needle holder and wherein said twisting allows proximal displacement and removal of said needle cover. - an injection needle having proximal and distal pointed ends, wherein the distal pointed end is arranged to penetrate a membrane arranged at the proximal end of a medicament container; - a tubular needle holder partially surrounding and fixedly connected to said injection needle, wherein said needle holder comprises on its outer circumferential surface ledges on a distal area and cut-outs on a proximal area; - a tubular cap comprising a distal part having container attachment means, a proximal part having bayonet fitting grooves on its outer circumferential surface, said tubular cap further comprising a central passage having bayonet fitting grooves (36, 38) on its inner circumferential surface adapted for receiving the ledges of the needle holder; - a tubular needle cover comprising on its inner circumferential surface, first ledges arranged to cooperate with the cut-outs of the needle holder, and second ledges arranged to cooperate with the bayonet fitting grooves of the cap; characterized in that said needle cover is arranged to be displaced axially by linear displacement in a distal direction in relation to said cap with the second ledges of the needle cover along said bayonet fitting grooves of said cap, wherein said needle holder is displaced axially distally due to the engagement between the first ledges of the needle cover and the cut-outs of the needle holder, that said needle cover is arranged to then be twisted whereby said needle holder is twisted, wherein said second ledges of said needle holder engages with transversal sections of said bayonet fitting grooves of said cap, preventing proximal displacement of said needle holder and wherein said twisting allows proximal displacement and removal of said needle cover.