This study examined the moderating effects of temperamental resistance to control on the link between development of sleep problems and development of externalizing behaviors over a 5-year period. Resistance to control was assessed with mothers' retrospective reports of temperament in infancy, provided when children were 5 years of age. Sleep problems were assessed with mother reports on an annual basis from age 5 to age 9. Externalizing behaviors were assessed with teacher reports on an annual basis from age 5 to age 9. A cross-domain latent growth curve model indicated that sleep problem trajectories were positively associated with externalizing behavior trajectories only for children high in resistance to control. In addition, resistance to control was positively associated with initial (age 5) sleep problems and initial (age 5) externalizing behaviors. The authors speculate that the development of sleep problems promotes the development of behavior problems for resistant children, whose self-regulatory abilities are especially tenuous. Implications for prevention and treatment of conduct problems are considered.Keywords sleep problems; externalizing behavior; temperament; self-regulation; childhood Sleep problems and daytime sleepiness are common in childhood. Kahn et al. (1989) reported that 43% of school-age children experienced persistent sleep problems, with 14% specifically experiencing persistent trouble sleeping. Sleep problems are also moderately stable in childhood (Gregory & O'Connor, 2002;Mindell, 1993). Kataria, Swanson, and Trevathan (1987) reported that the large majority of children in their sample with sleep problems continued to have sleep problems at follow-up 3 years later. Although many parents overlook sleep problems or underestimate the importance of good sleep habits for their children's wellCorrespondence concerning this article should be addressed to Jackson A. Goodnight (National Sleep Foundation, 2004;Stein, Mendelsohn, Obermeyer, Amromin, & Benca, 2001), children's sleep may be an important link between aspects of family functioning and children's adjustment (El-Sheikh, Buckhalt, Mize, & Acebo, 2006).Various methods have revealed links between sleep and externalizing problems. Using sleep problem items from the Child Behavior Checklist (CBCL; Achenbach, 1991a), Gregory and O'Connor (2002) found that sleep problems (e.g., sleeps less than other children, is tired during the day, nightmares) at age 4 predicted parent-reported aggression and attention problems in mid-adolescence. However, the reverse was not true. Sleep problems led to the development of externalizing behaviors, but externalizing behaviors did not lead to sleep problems. Using a sleep questionnaire rather than the CBCL to assess sleep problems, Gregory, Eley, O 'Connor, and Plomin (2004) found modest predictive associations between age 3 to 4 sleep problems and age 7 mother-reported conduct problems, controlling for age 3 to 4 conduct problems. In a cross-sectional study, Lavigne et al. (1999) found that s...