japhy and rads -- admit it! If it was "small" enough to get expunged, then they won't hold it against you when you admit to the incident. Remember, the courts are not want to expunge major matters.
Many law enforcement agencies have access to expunged records. This applies to DEA, the state boards, etc. In fact, many law enforcement agencies will specifically state (when asking that question), "You are required to list any conviction which has been set aside and dismissed or expunged, or where a stay of execution has been issued." This is a direct quote from the California P&S application, and I know (thru a buddy) that that the courts uphold their right to ask it. (Poor guy....he still regrets that mistake.)
California also only asks about "convictions" or "pending investigations." They legally can not ask about past arrests...because that goes against "innocent until proven guilty."
There are different codes entered about the agency which requests fingerprint clearances. If the agency is a law enforcement agency, then FBI will release more info than, say, to a potential employer checking on it.
Again -- this sounds so Johnnie Cochran -- "If you lie, they will deny." And if you get denied for a license application, that gets reported to the NPDB and is on your record the rest of your life.
You want to be a doctor; you want to be a professional. Be adult about it and admit it. They are willing to overlook a "youthful indiscretion" several years ago, assuming you have nothing on your record since then. But if you lie about it on your application, then you are seen as a person with a present propensity to lie. And that will get you in trouble.
(For example, if you got busted as a 19-yo with a joint....it's probably no big deal. (The folks reviewing your app probably inhaled themselves!) But if you lied about it last month when you filled out your app, that's a concern.)
Cheers