What is the likelihood of contracting hiv from protected anal intercourse?

Low...: The chances of acquiring an HIV infection from anal intercourse are very low if a condom is used. Addition of a spermicidal lubricant can also help to diminish the likelihood of HIV transmission. Condoms need to be used every time and not sporadically in order to be most effective and diminishing chances of spreading sexually transmitted diseases.

Depends: What is protected anal sex? What other practices are you engaging in that may result in exchange of body fluids. Anal sex is a high risk activity. See this site for more info. http://www.cdc.gov/hiv/resources/qa/transmission.htm.