OBJECTIVE: This study aimed to identify the predictors for treatment failure of medical management among admitted female patients diagnosed with pelvic inflammatory disease with tubo-ovarian abscess. METHODS: This was a retrospective nested case-control study, using chart review of all cases of pelvic inflammatory disease with tubo-ovarian abscess/complex (N = 49) admitted at the Department of Obstetrics and Gynecology, Philippine General Hospital from January 1, 2014 to December 31, 2018. RESULTS: Medical treatment failure was observed to be significantly higher (51.9%) among patients 40 years old and above as compared to patients less than 40 years old (13.6%). The risk of patients ≥40 years for failed management was 14x higher than those <40 years old (OR=14.00; 95% CI=1.06 to 185.5;p=0.04). The failed management group has significantly higher TOA size of 7.8 (7.8 ± 1.6) as compared to only 5.8 (5.8 ± 1.4) for medical treatment alone group. Correspondingly, those who failed have a significantly bigger volume of 120.4 ml (120.4 ± 84.5) as compared to only 55.2 ml (55.2 ± 40.6) for medical treatment alone group. Other predictive factors such as parity, admitting White blood cell count(WBC), C-Reactive Protein (CRP), and neutrophil-lymphocytic ratio(NLR) were all not significant. CONCLUSION: Tubo-ovarian abscess size of more than or equal to 7 cm, or a volume of more than or equal to 120 ml and advanced age of >40 were all predictive of failed response to medical treatment. Early recognition and intervention whether surgery or drainage may be beneficial to reduce morbidity and long-term sequelae of PID.