It is estimated that over one-half of all adolescent mothers receive inadequate prenatal care. Our objectives were to explore the barriers to care as perceived by adolescents and to develop a model to identify adolescents at risk for inadequate care. Structured interviews were conducted with 101 adolescents less than 17 years of age who delivered infants at an urban university hospital between September 1988 and January 1989. All the interviews were conducted within 48 hr of delivery by a single investigator. The Maternal Health Services Index was used to divide subjects into those who received inadequate care (Group 1, n = 37) and those who received intermediate or adequate care (Group 2, n = 64). Both groups were predominantly black (99%), poor (mean Hollingshead score = 2), and unmarried (99%). Groups 1 and 2 differed (p less than 0.05) in 12 variables pertaining to beliefs about prenatal care and course during the pregnancy. Of the 12 variables, 7 comprised a stepwise logistic regression model designed to maximally differentiate Groups 1 and 2--negative attitudes towards physicians (20% vs 6%), perceived importance of first trimester care (78% vs 94%), confusion about available prenatal services (24% vs 5%), lack of health insurance (41% vs 16%), exposure to pregnant friends (76% vs 95%), mean gestational age at recognition of pregnancy (15 wks vs 11 wks), and desire for an adolescent-only prenatal clinic (78% vs 58%). The adjusted odds ratios of the variables ranged in declining order from 15.4 to 4.7. The attributable risks, or etiologic fractions, of the variables ranged in increasing order from 0.19 to 0.49. Receiver-operating characteristic curve analysis of the model demonstrated a curve area of 0.89 +/- 0.04, significantly better than chance. We conclude that the model clarifies the barriers to care and helps identify pregnant adolescents who are likely to receive inadequate prenatal care.