The authors describe a case of the development of a pyosalpinx from a preexisting hydrosalpinx after uterine artery embolization (UAE) for leiomyomata. The hydrosalpinx preexisted the UAE procedure and did not cause the patient any symptoms or signs of infection. UAE was performed with standard technique and was technically as well as initially clinically successful. However, the patient presented 8 weeks post-UAE with a pyosalpinx and superinfection of the previously simple fluid collection, requiring treatment with hysterectomy and oophorectomy. A mechanism for the occurrence of this superinfection is proposed, and potential strategies to avoid this serious complication in the future are discussed.