It is normal for men to experience changes in erectile function, such as taking longer to achieve an erection. When the problem becomes persistent, it can be a sign of a physical or emotional problem.

Although in the past, impotence was commonly believed to be caused by psychological problems, it is now known that up to 90 percent of cases stem from physical problems, usually related to the blood supply of the penis.

Nearly all American men experience occasional impotence, and an estimated 30 million suffer from chronic impotence. But despite its prevalence, the condition is treatable in most cases.

Vasectomy is a permanent male birth control measure and a means of contraception used in many parts of the world.

Male menopause is a condition caused when testosterone levels decrease in aging men.

Detailed information on Peyronie's disease, including causes, symptoms, diagnosis, and treatment

A problem with the male is the sole cause, or a contributing cause, of infertility in about 40 percent of infertile couples.

Detailed information on sexually transmitted diseases, including causes, diagnosis, and prevention

A lot of us don't realize that chlamydia and other sexually transmitted diseases (STDs) can cause no symptoms, meaning you could have an STD and not know it.

AIDS is caused by the human immunodeficiency virus, which kills or impairs cells of the immune system and progressively destroys the body's ability to fight infections and certain cancers.

What's true and what's not when it comes to AIDS? Here's a look at some common myths surrounding HIV infection and AIDS.

The only safe sex is no sex, most health care providers say. But certain precautions and safe behaviors can minimize a person's risk of contracting a sexually transmitted disease.

Detailed information on puberty and the adolescent male

Detailed anatomical description of the prostate gland, including simple definitions and labeled, full-color illustrations

Detailed information on what males can expect during a physical examination

In an uncircumcised boy, the foreskin will begin to separate from the glans, or the tip of the penis. This happens naturally while the male is an infant. This is called foreskin retraction.

During adolescence, the developing teenager acquires the ability to think systematically about all logical relationships within a problem.

Adolescent attention often shifts to a more intense focus on social interactions and friendships expanding from same sex friends to same sex groups of friends to heterosexual groups of friends.

Your body usually tells you when you are in danger -- your heart races, you breathe hard, your palms sweat. But when it comes to sexually transmitted diseases (STDs), you may not have any warning signs.