I don't hide the fact that I'm bipolar; I just state it as a matter of fact thing in the same breath that I'm diabetic. I take meds for both. (Gee, pity you can't take you bipolar level like you can take your blood sugar!)

However, in some situations I do let people get to know me before I disclose because of the notoriety of mania -- and I educate people that bipolar isn't all mania and drama.