Background: The aim of this investigation is to evaluate the histologic results of biopsy in women with atypical squamous cells of undetermined significance (ASCUS) cytologic diagnosis. Materials and Methods: We reviewed a series of cases with ASCUS pap smears from March 1999 to Feb 2002 in Imam Khomeini Hospital (n= 104), Who had cervical biopsy indirected colposcopy (103) and in Onec endocervical biopsy obtained without colposcopy. In 60 patients before colposcopy and biopsy repeat pap smear was tabled. Results: Biopsy revealed 28.8% SIL (14 LSIL and 16 HSIL), 1 invasive carcinoma and 1 endometrial carcinoma. Pap smear repeated for 60 women before colposcopy examination, which 7 (11.7%) of them were normal. ASCUS persisted in 45 cases (75%) and 8 cases (13.3%) turned out to be SIL (6 LSIL, 2 HSIL) of 7 normal repeat smear, 2 marked as LSIL by biopsy. In colposcopic examination 22 of 103 (21.4%) had normal view which one of them was LSIL histologically. Conclusion: Based on these findings, it seems immediate colposcopy and directed biopsy are appropriate procedures for management of ASCUS and to detect underlying SIL.