The problem with the polygraph is that it is a crapshoot. Different personality types, different examiners, and other uncontrollable factors can lead to an incorrect result. Your general level of nervousness doesnt really affect the test so much, as EVERYONE is really nervous before their polygraph. Especially the first one. 

Might you fail the test even iff you didnt have anything too do with the theft? Yes you might. Or you may pass. What are the odds? Noone really knows. The polygraphers will tell you over 90% accurate. Those of us who have had careers ruined by the magic box are far less optimistic.

Just remember this.....just as the magician DOESNT REALLY make a coin disappear, the polygraph DOESNT DETECT LIES. Read the material on this site if you want to understand how the test works and how they lie to you more than you will ever lie to them.

I agree with George on one point, but not on another. I agree that you should get an attorney who knows his/her stuff. Any good, knowledgable attorney is going to tell you that taking a polygraph conducted on behalf of your employer is a bad idea. Now, sometimes the accused will commission their own polygraph examiner who will conduct a test in secret. If the accused passes that polygraph, then the pass is announced and proclaimed to the world, whereas if the accused fails, no one (usually) ever hears about it. If you pass THAT polygraph, then even if you somehow failed the one conducted by your employer's hired polygrapher, you can use one polygraph against the other, thereby negating anything negative.

I don't agree with George about reading The Lie Behind the Lie Detector and learning how to pass (beat) the polygraph. Countermeasures are as much of a crap shoot as some of these anti-polygraph people want you to believe the polygraph is.

In summary, if you're guilty, confess and take it like a man. If you aren't guilty, don't take the polygraph, but DO get a lawyer to back you up, and, as much as I hate to say it, DO reference this website because to the unexperienced the claims on this website are as credible as anything you'll hear from the pro-polygraph people, like myself. And if you are dumb enough to take the polygraph despite your attorney's advice, DON'T try countermeasures because if you are caught--even if you aren't guilty of the crime--you're sure going to look guilty.