Study Objective: Maternal serum screening is routinely offered to pregnant women in public hospitals in Victoria, Australia, regardless of their age. The aim of this study was to determine whether pregnant adolescents are less likely to make informed choices about undertaking this test than adult pregnant women. Design: Controlled, prospective design. Setting: Public hospital antenatal clinics in Victoria, Australia. Participants: Adolescents up to 20 years of age were recruited at young mothers’ clinics before they were offered second trimester maternal screening. They completed self-report questionaires prior to maternal serum screening and again after the screening result was known. Main Outcome Measures: A validated measure of informed choice was used to determine whether adolescents made informed choices about undertaking second trimester maternal serum screening. Results: Complete data were available for 147 adolescents. These data were combined with data from 85 adults which had been collected in an identical way. Ten percent of the adolescents made informed decisions about having the maternal serum screening, compared with 37% of the adult participant group (P < 0.05). Adolescent women were significantly less likely to make an informed choice than adult women, when relevant demographic and reproductive history variables were controlled for (adjusted OR = 0.25; P = 0.004; 95% CI for OR: 0.10, 0.63). Conclusion: Few pregnant adolescents made informed decisions about maternal serum screening. Clinicians face a challenge to improve adolescents’ knowledge about maternal serum screening.