Serosorting is a practice in the gay community where men try to select sexual partners who have the same HIV status as they do. It is a form of risk-reduction where guys who are HIV positive seek out only positive partners, and men who are HIV negative seek out partners who don't have HIV.

A subset of serosorting is called "selective positioning," which means "If I'm HIV positive and you are HIV negative, I'll take the higher risk-position and you be the one who sticks it in."

While some experts have credited serosorting with a drop in HIV among gay men, a number of gay men apparently use serosorting as justification for not wearing condoms, as in "As long as we are both positive, the worst has already happened and there's no reason to use condoms" or "If we're both negative, why use condoms?"

Some people feel that serosorting helps explain why the HIV rate has been decreasing while the rate of other sexually transmitted infections (STIs) has been rising among gay men--because all eyes are on HIV prevention with little concern about other STIs.

The trouble is, STIs like hepatitis, HPV, syphilis, gonorrhea and chlamydia can be much more serious in people who are already immunosuppressed or whose immune systems are compromised due to HIV infection. So there goes the "worst has already happened" justification.

Another concern for when HIV-positive guys are barebacking has been superinfection or dual infection. Superinfection is when an HIV-positive person becomes reinfected with a drug-resistant strain of HIV that his partner might bring to the table. Fortunately, this does not appear to be as big a risk as was originally thought, but it is still a risk.

As for the man who is HIV negative, how can can he be sure that the guy he just hooked up with on Craigslist really is HIV negative? Even if his new partner is being totally conscientious, HIV infection sometimes takes weeks or months to show up on tests.