if you use a condom and have sex with someone that has an std do you still have a chance of catching it from them
a small chance though, it depends more on the STD i think. For example something like herpes you could probably still catch.
If you have sex with someone who is HIV + and you use latex condoms 'properly', in addition to a water based lube i.e. Durex or K.Y, then chances you can contract HIV are none. HIV is a weak, fragile, hard to transmit virus, and is not granted from a single unprotected encounter. Latex is an excellent blocker to the virus. However, it remains your personal concern and fears. How would you handle this? Other infections can easily transmit to the other partner, even while you're using latex, because condoms fail to cover all the infectious areas. Examples are HSV 1 "Herpes Simplex a.k.a cold sores", HSV 2 "Genital Herpes", and HPV "Human Papilloma Virus"; the virus which causes genital warts in some cases, and which some strains are responsible for cervical cancer in females. These are the medical facts. Now it is your call.