An air/oil separating device for removing oil that has become entrained in blow-by gases passing through a crankcase of an internal combustion engine. The air/oil separating device includes a spiral element forming a spiral passageway and a perforated tube. As the air/oil stream passes through the spiral passageway and contacts its walls, a certain amount of the entrained oil is removed or scavenged such that it collects at the bottom of the spiral passageway. The treated air stream, now having less entrained oil, passes into the perforated tube and exits at an upper axial end, while the collected oil drains back into the crankcase via a lower axial end of the perforated tube. The air/oil separating device can be incorporated within a cap assembly also having an oil-fill cap and/or a PCV valve.