- Aims To determine the incidence and severity of acute pelvic inflammatory disease (PID) or tubo-ovarian abscess (TOA) in hospitalised women with and without a history of endometriosis. Methods Retrospective analysis of hospital records retrieved for all women hospitalised with PID or TOA between January 2008 and December 2011 in a tertiary referral centre. Women were compared with regard to a history of endometriosis for demographic, clinical and fertility data. Results 26 (15%) of the 174 women hospitalised due to PID or TOA were excluded because of age older than 45 years, leaving 148 for analysis. The mean age was 35.7 ± 9.3 years and mean duration of hospitalisation was 5.9 ± 3.7 days. The women were divided into two groups: Group 1 with endometriosis (n = 21) and Group 2 without endometriosis (n = 127). Women in Group 1 as compared with Group 2 were significantly more likely to have undergone a fertility procedure prior to being admitted to the hospital with PID (9/27 (45%) vs 22/121 (17%), P < 0.001); particularly in vitro fertilisation (IVF) (7/ 27 (33%) vs 12/121 (9%), P < 0.006); Women in Group 1 more frequently experienced a severe and complicated course involving longer duration of hospitalisation (8.8 ± 4.7 vs 4.4 ± 2.3 days, P < 0.0001) and antibiotic treatment failure (10/27 (48%) vs 8/121 (6%), P < 0.0001). Conclusions Pelvic inflammatory disease in women with endometriosis is more severe and refractory to antibiotic treatment, often requiring surgical intervention. It is likely that endometriosis is a risk factor for the development of severe PID, particularly after IVF treatment.