This study investigates the natural history of HPV and cervical neoplasia. At the initial recruitment visit, all women were administered a brief risk factor questionnaire, had blood collected and were given a pelvic examination if sexually active. At the time of the pelvic examination, a Pap smear and additional cervical cells were collected and used for additional monolayer smears (ThinPrep), HPV, and other testing. Based on these screening tests, women were referred to colposcopy, at which time a more detailed risk factor questionnaire was administered, additional cervical cells and blood were collected, and histological specimens were obtained, if indicated by the colposcopy. The longitudinal cohort consist of three distinct approximately equal groups of women without evidence of HSIL or cancer. The first group, women who at enrollment had evidence of low-grade cervical lesions (LSIL) or equivocal lesions and a sample of the remaining cohort members, were followed actively at 6-12 month intervals through their 7th anniversary in the cohort. The second group consists of women who were cytologically normal at enrollment but randomly selected for active follow-up. They were seen once after enrollment, at their 5th anniversary in the cohort. Women in this group with evidence of LSIL at the 5th anniversary visit were added to the first group described above and followed at 6-month intervals. The final group is of the remaining women in our cohort who were all cytologically normal at enrollment. They were followed passively via linkage to the cytology and tumor registries in Costa Rica. During follow-up, women with any evidence of progression to HSIL or cancer were referred to colposcopy, censored from the study, and treated by SSA clinicians using standard local protocols. The study is closed to accrual. At present, a cancer registry follow-up of women in the cohort is underway.