I tell them after I am hired, when it comes up naturally. I usually don't wait until I am sick. It usually comes in training like "by the way, I may have to step out to use the restroom because I have crohns. Please don't be offended if I step out while you are still speaking."
26 Year old married female law student (last year!!). Diagnosed w/ CD 4 years ago, IBS for over 10 years before that, which was probably the CD. I am sort of lactose intollerant too but can handle anything cultured and do well w/ lactose pills and lactaid. For crohns I am currently on Pentasa 4 pills/4x day and hysociamine prn. I also have bad acid reflux and have been on PPI's since age 13. I have been through prilosec, prevacid, and nexium. Currently I am on Protonix in the morning and Zantac at night. I also take a birth control pill to allow some fun in my life.