BACKGROUND: The triple marker test with maternal serum during 15-20 weeks gestation, based on AFP, hCG and uE3, is a useful screening technique for detecting chromosomal abnormalities and neural tube defect (NTD). However, the false positive rate has been reported from 4 to 8%. The purpose of this study was to evaluate whether or not women with a false positive result of the triple marker screening are at an increased risk for adverse outcomes other than chromosomal abnor-malities and NTD. METHODS: The study population was derived from 5,622 women undergoing triple marker screening at Mokdong Hospital between January, 1997 and August, 1999. A false positive was defined as a positive result of the triple marker test without further evidence of NTD or chromoso-mal abnormalities. The study group included 83 women whose results were a false positive and the 129 controls whose results were negative. The adverse outcomes included preterm delivery (<37 weeks), premature rupture of the membrane, pre-eclampsia, a low weight for the particular gesta-tion age (<10 percentile), a congenital anomaly and fetal death. RESULTS: The false positive rate of the triple marker test was approximately 1.5%. The overall inci-dence of adverse outcomes in the women with false positive result and those with a negative result were similar (30.1% vs 30.2%, respectively) (P > 0.05). However, adverse outcomes such as pla-cental abnormalities (8.4% vs 2.3%) and congenital anomalies (7.2% vs 0.8%) were more frequent in the women with a false positive result than women with a negative result s (P < 0.05). CONCLUSIONS: The results suggest that false positive results of the triple marker screening test do not appear to be associated with an increased risk for an adverse pregnancy outcome, but a careful evaluation for the placental and fetal abnormalities is necessary.