Objective: To assess retrospectively if there is a trend of change in the epidemiology of tubo-ovarian abscess (TOA) and to define the epidemiologic, clinical and laboratory risk factors associated with failed response to conservative antibiotic therapy. Study Design: The charts of 60 patients, admitted with clinically and sonographically diagnosed TOA between January 1995 and December 2000, were reviewed. On admission, all patients were treated with broad-spectrum antibiotics, and were divided into two groups according to the response to medical treatment. Forty-three patients, responding to antibiotic therapy, constituted group A, whereas 17 patients who did not respond and were further treated by sonographically guided drainage or surgery, were included in group B. The groups were compared with respect to patient characteristics, clinical and sonographic presentation, laboratory findings, duration of hospital stay and recovery rate of different pathogens from the endocervix. Results: The mean age of patients responding to medical therapy (group A) was significantly lower (39.6 ± 8.3) than the age of patients who did not respond (group B) (45.3 ± 6.6) (p = 0.02). The gravidity as well as the percentage of menopausal women were significantly increased in group B (p = 0.03 and p = 0.02, respectively). There was a significantly lower incidence of previous pelvic surgery and past history of PID in group B versus group A (p = 0.02 and p = 0.03, respectively), yet the duration of IUD use was significantly prolonged in group B (p = 0.02). The size of TOA, evaluated clinically and sonographically, was significantly increased in group B compared with group A (p = 0.04 and p = 0.009, respectively). Pelvic peritonitis was observed in 40% of group B patients and in none of group A patients (p = 0.0001). The only laboratory finding differentiating between the two groups was the mean sedimentation rate, being significantly higher in group B than in group A (p = 0.0005). The time interval from admission to afebrile condition as well as the duration of hospitalization were significantly shorter in group A (6.1 ± 2.3 days) than in group B (10.7 ± 4.7 days) (p = 0.00003). The incidence of positive culture from the endocervix was significantly higher in group B than in group A (p = 0.007). One hundred percent of patients in group B versus 65.2% of patients in group A were treated with triple agent therapy (p = 0.007). Conclusion: The results of the current study strengthen our previous assumption that there is probably a new trend in the epidemiology of TOA, occurring in older women, who do not present the traditional risk factors for pelvic inflammatory disease and TOA.