Background Adenocarcinoma in situ of the uterine cervix is a precursor to cervical adenocarcinoma and may coexist with both adenocarcinoma and high-grade squamous dysplasia (cervical intraepithelial neoplasia 2 and 3). Up to 60% of adenocarcinoma in situ lesions are detected incidentally following excisional biopsies performed for the treatment of cervical intraepithelial neoplasia 2/3. To date there are no data regarding risk factors for persisting or progressive cervical neoplasia in these patients. Objective We sought to investigate patient outcomes following incidentally detected cervical adenocarcinoma in situ after loop electrosurgical excision procedure or cold knife cone biopsy performed for the treatment of high-grade cervical intraepithelial neoplasia. Study Design We conducted a retrospective, population-based cohort study of Western Australian patients with an incidental diagnosis of adenocarcinoma in situ from 2001 through 2012. Primary outcomes were persistent or recurrent cervical intraepithelial neoplasia 2/3 and or adenocarcinoma in situ, and invasive adenocarcinoma during follow-up (<12 months) and surveillance (≥12 months) periods. Results The cohort comprised 298 patients, with 228 (76.5%) treated initially by loop electrosurgical excision procedure and 70 (23.5%) treated by cold knife cone biopsy. The mean age was 31.2 (range 18-68) years and the median length of follow-up was 2.4 (range 0.3-12.2) years. Overall, 11 (3.7%) patients had cervical intraepithelial neoplasia 2/3, 23 (7.7%) had adenocarcinoma in situ, and 3 (1.0%) had adenocarcinoma diagnosed during the follow-up and surveillance periods. Age >30 years, pure adenocarcinoma in situ lesions, and larger lesions (>8 mm) were associated with a greater risk of disease persistence or recurrence. Conclusion Following the incidental detection of adenocarcinoma in situ, age >30 years, pure adenocarcinoma in situ lesions, and lesions >8 mm were significantly associated with disease persistence/recurrence. In younger women, incidentally detected adenocarcinoma in situ that coexists with cervical intraepithelial neoplasia 2/3 and is <8 mm extent with clear margins may not require reexcision.