IStock Photo 8546982 © Joseph Luoman

You like her. She likes you. You’ve gone on a few dates, felt that fluttering excitement and ineffable chemistry, and now it’s time to take the next step. You want to have sex.

Lord knows there are plenty of rough spots when you get to know someone intimately. But before you even slip between the sheets, one of the trickiest and most critical questions in your relationship comes into play: Is your partner-to-be free of STDs? For that matter, are you?

Yes, your acutely embarrassing health teachers drilled into your head the necessity of practicing safe sex (if not total abstinence) and getting tested for sexually transmitted diseases (STDs). Sitting in class wishing for this special torture to be over, you might have assumed you’d always get yourself and your partner tested before laying a finger on each other, or at least ask about his or her sexual history and expect an honest answer.

But talking about open sores, pubic lice and genital warts is just about the unsexiest thing imaginable. And the thought of contracting—or already unknowingly harboring—one of these infections is pretty darn frightening. Certain you can’t have anything, afraid you’re not as healthy as you think, wary of being seen as irresponsible or promiscuous, believing in your own carefulness or invincibility, or wanting to trust your partner’s word, you might be tempted to take your chances.

So what are your chances? You’ve heard statistics on the estimated prevalence of HIV/AIDS and other STDs. But what about the likelihood that people are aware of their own health status (especially when infections can lurk without causing symptoms) and tell the truth to their partners?

According to the US Centers for Disease Control, the odds a man aged 15-44 has been tested for HIV and other STDs in the past year are 1 in 14.08 (7%). The odds for a woman in the same age group are slightly higher, at 1 in 10.53 (9.5%). The odds a guy 15-44 has ever been tested for HIV are 1 in 2.15 (46%); a gal, 1 in 1.82 (55%).

Now, what about honestly reporting the results of those tests to your partner? In a 2008 survey of 75,000 men at AskMen.com, 2% of respondents admitted they’d lied about their sexual health. But before you cry proof that men are pigs, consider that an accompanying survey of 10,000 women got the same result.

Okay, you might say, that means I’ve got a 98% chance my partner is telling the truth. Well, not quite. The same survey found that only 24% of male respondents had ever been tested for sexually transmitted diseases. (Sorry, guys; the women’s survey didn’t ask about STD testing.) Of those, slightly less than half were STD-free. So more than three-quarters of survey-takers can’t tell the truth, because they don’t know what it is—even if they’re “sure” they’re clean.

Something to think about before you and your new sweetheart switch off the bedroom lights.