Introduction Fallopian tube carcinoma is a rare gynecological malignancy with low accuracy detection preoperatively. The symptoms are unspecific and imaging can be misleading. Since it was first described in 1847, there have been only a little over 2000 case reports. Case presentation This case report describes a 66-year-old Caucasian woman who presented with progressive diffuse abdominal pain, without other symptoms. After abdominopelvic magnetic resonance imaging, she was sent to the Portuguese Oncology Institute of Oporto with the suspicion of peritoneal carcinomatosis of unknown primary tumor. Due to a pelvic palpable mass (calcified giant uterine fibroid) she was directed to the Gynecology team. Surgery was performed and a large mass in her upper abdomen was identified. The extemporary examination revealed a high-grade adenocarcinoma. During surgery a small change of color and consistency of her left fallopian tube was noted and unilateral adnexectomy was performed. After pathologic and immunohistochemistry tests, the diagnosis of fallopian tube carcinoma with peritoneal dissemination was made. Conclusions This case is very unique in the way that a small primary fallopian tube carcinoma was able to disseminate to the upper abdominal quadrant with little pelvic dissemination. The symptoms and imaging were unspecific. Although a rare occurrence, we should not forget fallopian tube carcinoma in the differential diagnosis of peritoneal carcinomatosis, even in the absence of Latzke’s triad.