The uterus is the central organ of a woman’s reproductive system. This hollow, muscular chamber houses and protects a developing fetus during pregnancy. The entrance to the uterus, called the cervix, is a muscular canal located inside the vagina. The exterior of the cervix is continuous with the vagina and is lined with flat, or squamous cells, whereas the interior of the cervix is lined with tall or columnar cells. At the junction of these two cell types, the squamo-columnar junction, abnormal cellular growth, or cervical dysplasia, can occur. In mild dysplasia, or CIN I, only a few cells may be abnormal. However, when about 1/2 of the thickness of the cervical lining is affected the dysplasia is called moderate or CIN II. Dysplasia becomes severe, or CIN III, when the full thickness of the cervix has abnormal cells. This condition is called carcinoma-in-situ and if left untreated can progress into invasive cervical cancer. During a Pap smear, which tests for cervical dysplasia, a small sample of cells are scraped from the surface of the cervix. If abnormal cells are detected on analysis of the cells, a colposcopy will be performed. During colposcopy the cervix is examined with a magnifying lens and small samples of tissue are biopsied for further pathologic evaluation. There are several methods for treating cervical dysplasia, depending on the severity. Since early detection is key to the prevention of cervical cancer, all women should have Pap smears performed on a yearly basis, or according to their doctor’s recommendation depending on the woman’s age and medical history.