Objective: To assess the clinical value of a single serum CA-125 level in women presenting with symptoms of threatened abortion from 5 to 12 weeks gestation. Study design: Hundred women with symptoms of threatened abortion from 5 to 12 weeks gestation were allocated to 3 subgroups: Group I (n = 48) abdominal pain only Group II (n = 31) abdominal pain and vaginal bleeding, and Group III (n = 21) vaginal bleeding only. The control group (n = 100) was women undergoing a normal pregnancy of comparable gestational age. In all patients, serum CA-125 levels were determined with the commercially available chemiluminometric method.