To evaluate the performance of routine endocervical curettage (ECC) for diagnosing high-grade cervical intraepithelial neoplasia (CIN) 2 or worse and additional precancers not otherwise detected by ectocervical biopsies. In a secondary analysis of the Biopsy Study, a cross-sectional study conducted between 2009 and 2012 at the University of Oklahoma Health and Sciences Center that found an incremental increase in detection of cervical precancers by multiple biopsies at colposcopy, ECC was performed in most women aged 30 years or older. Cervical intraepithelial neoplasia 2 or worse yield by ECC alone was evaluated in analyses stratified by cervical cytology (atypical squamous cells of undetermined significance [ASC-US] or low-grade squamous intraepithelial lesions [LSIL] compared with atypical squamous cells, cannot exclude high-grade squamous intraepithelial lesions [ASC-H] or high-grade squamous intraepithelial lesions [HSIL] or worse), colposcopic impression (less than high-grade compared with high-grade), human papillomavirus (HPV)-16 infection status, whether the examination was satisfactory, and by ECC indications per the current guidelines for cervical cancer screening. The diagnostic value of ECC for detecting additional disease was evaluated by the number of lesion-directed ectocervical biopsies. Of the 204 women aged 30 years or older, 181 (88.7%) underwent ECC. Overall ECC detected 14.4% CIN 2 or worse (95% CI 10.0-20.2%). Endocervical curettage was more likely to find disease in the endocervix among women with high-grade cytology, positive HPV-16 infection, or high-grade colposcopic impressions (respective P values <.05). Among women with ASC-US or LSIL cytology, those with an unsatisfactory examination had a 13.0% CIN 2 or worse yield on ECC (95% CI 6.1-25.7); when colposcopic examination was normal or satisfactory with visible abnormal lesions, ECC detected less than 5% CIN 2 or worse in the endocervix. An ASC-H or HSIL or worse cytology was associated with a CIN 2 or worse yield of 25.8% by ECC (95% CI 16.6-37.9%). However, ECC found only 3.9% (95% CI 1.9-7.8%) additional CIN 2 or worse beyond the cumulative disease detected by up to four biopsies of visible acetowhite ectocervical lesions. Additional CIN 2 or worse yield by ECC increased when fewer lesion-directed biopsies were taken (P<.05). The additional yield of CIN 2 or worse by ECC in a colposcopy with up to four ectocervical biopsies was low. Based on our findings, we recommend routine ECC be performed in women aged 45 years old or older with HPV-16 infection and in any woman aged 30 years or older with HSIL or worse or ASC-H cytology, high-grade colposcopic impression, or ASC-US or LSIL cytology and an unsatisfactory examination. ClinicalTrials.gov, NCT00339989.