Cervical intraepithelial neoplasia, or CIN, is the abnormal growth of precancerous cells in the cervix. Most cases of CIN remain stable, or are eliminated by the host's immune system without intervention. However a small percentage of cases progress to become cervical cancer, usually cervical squamous cell carcinoma, or SCC. The major cause of CIN is infection with the sexually transmitted human papillomavirus (HPV), usually the high-risk HPV types 16 or 18.

The earliest microscopic change corresponding to CIN is dysplasia of the epithelial or surface lining of the cervix, which is essentially undetectable by the woman. Cellular changes associated with HPV infection, such as koilocytes, are also commonly seen in CIN. It is usually discovered by a screening test, the Papanicolaou or "pap" smear. The purpose of this test is to diagnose the disease early, while it has not yet progressed to invasive carcinoma, and thus is easy to cure. Though epithelial dysplasia may regress spontaneously, persistent lesions must be removed, either with surgery, chemical burning, heat burning, burning with laser, or freezing (cryotherapy).