OBJECTIVE: To define the predictors discriminating between patients developing tuboovarian abscess (TOA) and those with non-TOA acute pelvic inflammatory disease (PID) on the day of admission to the hospital. STUDY DESIGN: One hundred sixty-three patients were evaluated and divided into 2 groups: 42 patients diagnosed with clinical and sonographic evidence of TOA and 121 diagnosed with PID. Relying upon the significant differences between the 2 groups, cutoff levels yielding the best degree of discrimination were determined. RESULTS: A palpable adnexal mass in a woman older than 42 years and erythrocyte sedimentation rate > 50 mm/h were the best predictors of TOA. There was no difference in the mean temperature or number of sick days prior to hospitalization. CONCLUSION: Our results suggest that there are parameters that can be used as predictors of TOA and prolonged hospital stay. These parameters can advance the beginning of more aggressive antibiotic treatment.