CONTEXT: Rates of rapid second births among low-income black adolescent mothers range from 20% to 50%. Most efforts to prevent rapid second births have been unsuccessful. OBJECTIVES: There were 4 objectives: (1) to examine whether a home-based mentoring intervention was effective in preventing second births within 2 years of the adolescent mother's first delivery; (2) to examine whether greater intervention participation increased the likelihood of preventing a second birth; (3) to examine whether second births were better predicted from a risk practice perspective or a family formation perspective, based on information collected at delivery; and (4) to examine how risk practices or family formation over the first 2 years of parenthood were related to a second birth. DESIGN: We conducted a randomized, controlled trial of a home-based intervention curriculum, based on social cognitive theory, and focused on interpersonal negotiation skills, adolescent development, and parenting. The curriculum was delivered biweekly until the infant's first birthday by college-educated, black, single mothers who served as mentors, presenting themselves as 'big sisters.' The control group received usual care. Follow-up evaluations were conducted in the homes 6, 13, and 24 months after recruitment. METHODS: Participants were recruited from urban hospitals at delivery and were 181 first time, black adolescent mothers (< 18 years of age); 82% (149 of 181) completed the 24-month evaluation. RESULTS: Intent-to-treat analyses revealed that control mothers were more likely than intervention mothers to have a second infant. The complier average causal effect was used to account for variability in intervention participation. Having > or = 2 intervention visits increased the odds of not having a second infant more than threefold. Only 1 mother who completed > or = 6 visits had a second infant. At delivery of their first infant, mothers who had a second infant were slightly older (16.7 vs 16.2 years) and were more likely to have been arrested (30% vs 14%). There were no differences in baseline contraceptive use or other measures of risk or family formation. At 24 months, mothers who had a second infant reported high self-esteem, positive life events, and romantic involvement and residence with the first infant's father. At 24 months, there were no differences in marital rates (2%), risk practices, or contraceptive use between mothers who did and did not have a second infant. Mothers who did not have a second infant were marginally more likely to report no plans for contraception in their next sexual contact compared with mothers who had a second infant (22% vs 8%, respectively). CONCLUSIONS: A home-based intervention founded on a mentorship model and targeted toward adolescent development, including negotiation skills, was effective in preventing rapid repeat births among low-income, black adolescent mothers. The effectiveness of the intervention could be seen after only 2 visits and increased over time. There were no second births among mothers who attended > or = 8 sessions. There was no evidence that risk behavior or contraceptive use was related to rapid second births. There was some evidence that rapid second births among adolescent mothers were regarded as desirable and as part of a move toward increasing autonomy and family formation, thereby undermining intervention programs that focus on risk avoidance. Findings suggest the merits of a mentoring program for low-income, black adolescent mothers, based on a relatively brief (6-8 sessions) curriculum targeted toward adolescent development and interpersonal negotiation skills. [ABSTRACT FROM AUTHOR]