Commonly used preoperative diagnostic procedures were analyzed for their ability to predict the presence of early ectopic pregnancy. Patients presenting to the emergency room with acute onset of pelvic pain were evaluated with culdocentesis, pelvic ultrasonography, and qualitative serum and urine pregnancy testing. Clinical examination and urine pregnancy testing were found to be poor predictors of either the presence or absence of an early ectopic pregnancy. The combination of a sensitive serum human chorionic gonadotropin (hCG) determination and pelvic ultrasonography accurately predicted ectopic pregnancy in 93% of proved cases. This predicted accuracy was superior to that of culdocentesis alone or in combinations of culdocentesis and ultrasound or qualitative serum pregnancy testing.