Paratubal cysts (PTCs) are generally incidentally detected in pregnancy. However, paratubal cystadenomas in pregnant women are very rare cases who are reported individually. An unusually giant case of paratubal cystadenoma in a pregnant woman is presented here. A 27-year-old woman presented to our department for a routine pregnancy checkup. A giant cystic mass accompanying a 17-week gestation was detected on examination. During laparotomy, a huge right-sided PTC was resected. Histopathological evaluation revealed a benign cystadenoma originating in the ipsilateral paratubal space. PTCs are often denoted as being benign. Neoplastic transformation or malign potential will change the course of follow-up and the patients' prognosis. Treatment with surgical excision in the second trimester can safely prevent such associated adverse conditions. In conclusion, gynecologists should be careful for causes of adnexal masses in a woman with an intrauterine pregnancy. PTCs also tend to show accelerated growth patterns during pregnancy.