Hyperplasia of mesonephric remnants in the uterine cervix is an unusual condition that is often misdiagnosed as adenocarcinoma. The rare mesonephric carcinoma can be confused with more common forms of cervical adenocarcinoma. We studied 49 specimens of cervix containing mesonephric remnants, or lesions derived from them, in women 21 to 72 (mean, 38) years of age. Four cases were classified as mesonephric remnants, 31 as lobular mesonephric hyperplasia, eight as diffuse mesonephric hyperplasia, two as mesonephric ductal hyperplasia, and four as mesonephric carcinoma. In the nonneoplastic cases, the lesion was unrelated to symptoms that resulted from excision of cervical tissue and, except in one case, did not produce a detectable mass. In two cases of carcinoma, the patient presented with bleeding; in one case, the patient presented with pelvic relaxation. The manner of presentation was not known in the fourth case of carcinoma. Twenty-eight patients with mesonephric remnants or hyperplasia underwent hysterectomy; 15 had a cone biopsy; one underwent excision of the cervical stump; and one had only a cervical biopsy. None of these patients has had a recurrence. All four patients with carcinoma had a hysterectomy; three of them died of carcinoma 2 years and 10 months, 7 years, and 9 years after diagnosis, respectively. Correct classification of mesonephric lesions is imperative for appropriate patient management.