Introduction: The purpose of this study was to delineate the association between endometriosis and pelvic inflammatory disease (PID) and the prevalence of this coexistence. Materials & Methods: The records of all patients with endometriotic ovarian cysts treated at the 3rd Department of Obstetrics and Gynecology of the University of Athens and in “Lito” Maternity Hospital of Athens from 2000 through 2007 were reviewed. Results: During this 7-year period 720 women underwent surgery due to endometriotic ovarian cysts. The average age was 40.9 years (range: 17-70). Median diameter of the cysts was 4.495 cm and 59% were located in the right ovary. PID was identified in 21 (2.9%) cases. The average age of these women was 31 years (range: 21-39). Half of the women presented with fever (10/21; 47.6%). Ultrasound examination was performed in all women, followed by laparoscopy. In 47.6% (10/21) the PID abscess was located in the right ovary and the rest (52.38%) in the left. The mean diameter of the endometriotic cysts in these women was 3.52 cm. Laparoscopy was the treatment of choice in all the women with the exception of five cases, where due to technical difficulties during laparoscopy, a laparotomy was performed. In all the cases with PID, abscesses were evacuated laparoscopically. No operative complications were observed. Conclusions: Endometriosis and PID are two conditions that can easily confuse the physician in setting the diagnosis, especially in the situation where they co-exist. In our study we report that the prevalence of PID in women with endometriosis is sufficiently higher than the prevalence in the general population.