Summary: A prospective cohort of pregnant adolescent patients who planned to deliver at 1 of 3 Perth metropolitan hospitals was studied; 1 subgroup of this cohort was offered universal screening for cervical chlamydial infection and Pap-smear abnormalities (screened), and the remainder of the cohort were offered screening at the discretion of the attending medical staff (control). High prevalences of both chlamydial infection (27%) and Pap-smear abnormalities (38%) were detected in the screened cohort. The majority of Pap-smear abnormalities were inflammatory atypia, but high-grade Bethesda lesions were also diagnosed. In the control group, the prevalence of positive swabs and abnormal Pap-smear reports in those tested was also high (22% and 35% respectively), but significantly fewer patients were tested (18% and 33% respectively in the control group, compared to 92% and 94% in the screened group; both p < 0.001). Screening and treatment of chlamydia was associated with a significant decrease in the incidence of newborn febrile morbidity (10% versus 25%; p = 0.02). In view of the high prevalence of positive results, it is cost-effective to offer universal screening in this setting. Failure to introduce a specific screening policy can result in a significant number of patients being denied the advantages of diagnosis and treatment.