A fluid sampling or infusion device for an extracorporeal blood treatment apparatus comprises: a protective body (29) having a first aperture (30) and a second aperture (31) and comprising a connecting device (28) configured to connect, optionally in removable manner, the protective body (29) to a sampling or infusion site (20) of the extracorporeal blood treatment apparatus (1)； a needle assembly (33) comprising a first end (34) connected or connectable, optionally in removable manner, to a syringe (22) and a needle (35) protruding from a second end opposite the first end (34). The needle assembly (33) is movable inside the protective body (29) between a first position and a second position. In the first position the needle (35) is completely enclosed by the protective body (29) and in the second position the needle (35) protrudes from the second aperture (31) to pierce the sampling or infusion site (20) .
