Background: Pyosalpinx as a cause of acute appendicitis is very rare. We report the first case of a right pyosalpinx causing an extrinsic compression of the appendiceal lumen and consequently an acute appendicitis following an obstruction. Case presentation: A 32 year old female from the North west region of Cameroon, presented with an acute exacerbation of a mild chronic right iliac fossa pain over a 2 day duration. She underwent exploratory laparotomy and intraoperative findings were a bilateral pyosalpinx, with the right fallopian tube adhering to the caecum and the terminal ileum, and obstructing the lumen of an inflammed appendix. A classical appendectomy and a right salpingectomy were done. The post-operative period was uneventful and she returned after 2 weeks for a follow-up visit with no further complaints. Conclusion: We describe to the best of our knowledge, the first case of an acute appendicitis caused by an extrinsic obstruction of the appendiceal lumen by a pyosalpinx. The close proximity of the caecum to the right fallopian tube most likely accounted for this occurrence. Although a rare entity, physicians should always keep in mind very rare causes of an acute appendicitis to guide management. This case highlights the shortcomings of pelvic ultrasonography in the diagnosis this condition. A pelvic computed tomography scanning should therefore be sought in case of a doubtful pelvic ultrasonography result. Finally, there is an urgent need to improve the awareness on sexually transmitted infections in our setting.