Chancroid is a painful STD that causes ulcers around the genitals. It's easily cured and very rare in the U.S.
Chlamydia is the most common STD. You can cure it with antibiotics, but many don't have symptoms.
Genital herpes is caused by a virus. It produces painful lesions, usuallly below the waist. There is no cure for genital herpes.
Gonorrhea is a common STD that's becoming increasingly difficult to cure.
Hepatitis is a virus that causes liver inflammation. Hepatitis C is among the most dangerous. It can cause cirrhosis, liver cancer and liver failure.
HIV is the virus that causes AIDS. It destroys your body's ability to fight off infections. It can be treated with medicine.
Every sexually-active adult probably has HPV, but most never experience any symptoms or complications.
Syphilis is one of the most dangerous and one of the most easily-cured STDs -- if you know you have it.
Trichomoniasis is a sexually-transmitted disease caused by a parasite. It's more common in women than in men and is easily cured.