The invention concerns a piston compressor, particularly a hermetically enclosed refrigerant compressor, with at least one cylinder a piston reciprocating in said cylinder, the piston being connected with a driving rod via a piston pin and having in its outer jacket surface a circumferential lubrication groove, the piston pin having a longitudinal bore, which is connected with a lubricant source. It is endeavoured to improve the lubrication. For this purpose, the longitudinal bore is open downward in the gravity direction and has a ventilation opening upward.