Can we tell ghost stories now?

I've got several. Hospitals are usually crawling with them. My hospital now is a relatively new one (only 16 years old), so there aren't many stories here, but the old Northwestern Hospital in Chicago was over 100 years old and in the building of a former orphanage. Lots of ghost stories there.
My most memorable was something that happened to me in the middle of the night on-call. The hospital had 8 inpatient floors, but a 9th floor that led to the helicopter pad and was used just for storage (you needed a special key to get up there). The ICU was on the 2nd floor and the staff elevator that went all the way up to 9th floor was just outside the ICU. One night, sometime around 2-3am, one of the older security guards got off the elevator and stumbled into the ICU white as a sheet. He told me that he was doing his night rounds, checking on the floors. He took the elevator up to the 9th floor and was going to work his way down. When the elevator opened on 9, there was a young woman at the door. He nodded to her, thought it was somewhat strange that someone was up there (but people did occassionally go there to get supplies), but didn't think much of it. She entered the elevator and he stepped out. He stepped out of the elevator only a few feet to take a quick look around. He saw that there was no one up there, and turned back to the still open elevator door. The young woman was gone. Just disappeared. He got in the elevator and forced it to go down all the way to the ICU. ICUs are typically the most bright, well-lit, and active parts of the hospital at night. The guy was a mess. I would be surprised if he ever went back up there.