Our purpose was to determine the effectiveness of 5-fluorouracil (5-FU) in the treatment of vaginal intraepithelial neoplasia (VAIN).The study was performed in 30 patients with a mean age of 54 years and previous diagnoses from reviewed records and histopathology slides selected from a group of 65 patients with VAIN from 1980 to 1998. Patients received intravaginal treatment with 5-FU, 1.5 g once weekly for 10 weeks and all patients were followed up for at least 2-years. Papanicolaou smear and colposcopy were performed, as was biopsy when indicated.Twenty eight (93%) patients with VAIN had prior or concurrent anogenital squamous neoplasia, including 5 with invasive cervical carcinoma and 23 with cervical intraepithelial neoplasia. In 23 of 30 treated patients (77%), VAIN went into remission after a single treatment; in 3, (10%), it went into remission after two treatment; 3 (10%) had recurrent VAIN 3; and in 1 (3%) it progressed to invasive vaginal cancer. The treatment was well tolerated.The 5-FU is an option choice for VAIN treatment. It is effective, with minimal slide effects. Its use should be confined to treating extensive or multifocal high-grade VAIN.