We wished to compare the relative reproducibility and validity of cervical intraepithelial neoplasia (CIN) 2 and CIN3 diagnoses. In a population-based cohort study (1993-2001) of human papillomavirus (HPV) and cervical neoplasia in Costa Rica, we compared community pathologists' diagnoses with those of the 2 independent reviewers from the United States (total, n = 357). As measures of validity, we correlated primary and review diagnoses with HPV positivity and cytological interpretations. Two review pathologists agreed with 84% and 81%, respectively, of initial diagnoses of CIN3 compared with 13% and 31% of CIN2. The CIN3 diagnoses made by review pathologists were 94% oncogenic HPV positive, compared with 72% of CIN2 diagnoses. Eighty-one percent of CIN3 diagnoses versus 61% of CIN2 were correlated with high-grade cytological interpretations. The CIN3 is a substantially more reproducible diagnosis that can be validated more frequently with HPV tests and cytological interpretations than CIN2.