The cervix is the lower part of the uterus (womb). The uterus is divided into two parts. The upper part or body of the uterus is where a fetus grows. The cervix connects the body of the uterus to the vagina (birth canal). The part of the cervix closest to the body of the uterus is called the endocervix. The part next to the vagina is the ectocervix.

Cancer of the cervix (also known as cervical cancer) is a cancer beginning in the lining of the cervix. Cervical cancers do not form suddenly. There is a gradual change from a normal cervix to precancer to cancer. Some women with precancerous changes of the cervix will develop cancer. This usually takes several years but sometimes can happen in less than a year. For some women, precancerous changes may go away without any treatment. More often, if these precancers are treated, true cancers can be prevented. Precancerous changes and specific types of treatment for precancers are discussed in the section "Can Cancer of the Cervix Be Prevented?"

Precancerous changes can be separated into several categories based on how the cells of the cervix look under a microscope. There are several systems for naming and describing these categories of potentially cancerous or precancerous changes. These systems are also discussed in the section on "Can Cancer of the Cervix Be Prevented?"

There are two main types of cervical cancers: squamous cell carcinoma and adenocarcinoma. These, as well as rarer types of cervical cancer and cervical precancers, are classified according to how they look under a microscope. About 85%-90% of cervical cancers are squamous cells carcinomas. They begin in the ectocervix, most often at its border with the endocervix. The remaining 10%-15% of cervical cancers are adenocarcinomas. Cervical adenocarcinoma develops from the mucus-producing gland cells of the endocervix. Less commonly, cervical cancers have features of both squamous cell carcinomas and adenocarcinomas. These are called adenosquamous carcinomas or mixed carcinomas.

Precancerous and cancerous changes of the cervix can usually be found by the Pap test (also called a Pap smear). This test involves scraping some cells from the surface of the cervix and looking at them under a microscope. Since precancers and very early cervical cancers are nearly 100% curable, this test can prevent nearly all deaths from cervical cancer. The Pap test is explained more completely in the section called "Can Cancer of the Cervix Be Prevented?".