Simple Summary: In situ/microinvasive adenocarcinoma of the uterine cervix represents the majority of cervical glandular lesions and can be treated conservatively. In contrast to squamous lesions, approximately 15–20% of glandular disease may be HPV-negative and therefore associated with a worse prognosis. Furthermore, up to 4% of cases may show recurrence after three years of follow-up. Given the abovementioned risk, knowing the predictive factors of disease recurrence becomes crucial for post-treatment management. In the present study, HPV testing in follow-up was the best predictor for recurrences in women with in situ/microinvasive AC undergoing conservative treatment. So, its use in clinical practice is of pivotal importance. However, attention should be paid to non-high-risk HPV women in follow-up with non-usual-type histopathology, given that it seems to represent a sub-population at increased risk of recurrences. Objective: The present study aimed to assess long-term follow-up outcomes in women with in situ/microinvasive adenocarcinoma (AC) of the uterine cervix treated conservatively. Methods: Retrospective multi-institutional study including women with early glandular lesions and 5-year follow-up undergoing fertility-sparing treatment. Independent variables associated with recurrence were evaluated. Logistic regression analysis and Kaplan–Meier survival analysis with Logrank test were performed. Results: Of 269 women diagnosed with in situ/microinvasive AC, 127 participants underwent conservative treatment. During follow-up, recurrences were found in nine women (7.1%). The only factor associated with recurrence during follow-up was positive high-risk Human Papillomavirus (hr-HPV) testing (odds ratio 6.21, confidence interval 1.47–26.08, p = 0.012). HPV positivity in follow-up showed a recurrence rate of 21.7% against 3.8% in patients who were HPV-negative (p = 0.002, Logrank test). Among women with negative high-risk HPV tests in follow-up, recurrences occurred in 20.0% of non-usual-type histology vs. 2.1% of usual-type cases (p = 0.005). Conclusion: HPV testing in follow-up is of pivotal importance in women with early glandular lesions undergoing conservative treatment, given its recurrence predictive value. However, women who are high-risk HPV-negative in follow-up with non-usual-type histopathology may represent a sub-population at increased risk of recurrences. Further studies should confirm these findings. [ABSTRACT FROM AUTHOR]