Background. Traditionally, hysterectomy is considered definitive therapy for cervical adenocarcinoma in situ (AIS) in women beyond childbearing. Case. A 45-year-old gravida 2, para 2 patient presented with cervical dysplasia and on pathology review of the large loop excision procedure cervical adenocarcinoma in situ was diagnosed. She underwent extrafascial hysterectomy and bilateral salpingooophorectomy. Final pathology revealed adenocarcinoma in situ with negative margins. Twenty-eight months later, she presented with right lower extremity deep venous thrombosis. A computed tomography (CT) scan of the abdomen and pelvis showed a pelvic sidewall mass. A CT-guided biopsy of the mass was consistent with invasive adenocarcinoma of the endocervical type. She underwent combination therapy with weekly cisplatin and extended field radiation therapy. Conclusion. This case depicts another example of the unpredictable nature of cervical AIS. Despite undergoing definitive surgery, a residual focus of disease may remain leading to invasive adenocarcinoma. Close follow-up is required of all patients diagnosed with AIS because the disease is poorly understood. Background. Traditionally, hysterectomy was considered definitive therapy for cervical adenocarcinoma in situ (AIS) in women beyond childbearing. Case. A 45-year-old gravida 2, para 2 patient presented with cervical dysplasia and on pathology review of the large loop excision procedure Cervical adenocarcinoma in situ was diagnosed. She underwent extrafascial hysterectomy and bilateral salpingooophorectomy. Final pathology revealed adenocarcinoma in situ with negative margins. Twenty-eight months later, she presented with right lower extremity deep venous thrombosis. A computed tomography (CT) scan of the abdomen and pelvis showed a pelvic sidewall mass. A CT-guided biopsy of the mass was consistent with invasive adenocarcinoma of the endocervical type. She underwent combination therapy with weekly cisplatin and extended field radiation therapy. Conclusion. This case also another example of the unpredictable nature of cervical AIS. Despite undergoing definitive surgery, a residual foc us of disease may remain leading to invasive adenocarcinoma. Close follow-up is required of all patients diagnosed with AIS because the disease is poorly understood.