The study found that experiencing sexual debut was associated with delinquent behavior 1 year later. Also, the adolescents who had an early sexual debut relative to their peers were at higher risk of later delinquent behavior compared to those whose sexual-debut timing was similar to that of their peers. Adolescents whose sexual debut was later than that of their peers were the least likely to engage in delinquent behavior. This protective effect of late sexual debut apparently persisted for several years. The authors suggest that early sexual debut is likely to occur before most adolescents are developmentally prepared to deal with the emotional and social consequences of engaging in sexual intercourse. The study sample was limited to adolescents who completed all waves of the in-home interviews of the National Longitudinal Study of Adolescent Health (1994-95, 1996, and 2001-2002). The first wave of the survey involved all students who were attending 132 high schools and their "feeder" middle schools (grades 7 through 12). A randomly sampled subset of approximately 20,000 of these students was subsequently interviewed at home (Wave I in-home interview), as were 1 of their parents. A second wave of in-home interviews conducted in 1996 involved a follow-up response for the Wave I in-home respondents (n=14,738). A third set of interviews was conducted with the Wave I in-home respondents between August 2001 and April 2002 (n=15,197). At the third wave, most respondents were between 18 and 26 years old. 4 tables and 50 references