Results indicated that youths who worked intensively in formal jobs were more likely to be involved in delinquent activities and to abuse substances more often than youths who did not work intensively in formal jobs. On the other hand, no evidence was found to indicate that a transition into intensive work in formal jobs, in comparison to moderate work or no work, during the school year led to an increase in delinquency or substance use. The findings on informal jobs also indicated that informal work might increase delinquency involvement and substance use among a varied sample of youth. The findings have implications for cities across the country that spent millions of dollars on summer job programs in an effort to curb delinquency. The current study actually revealed that summer-only employment might increase delinquency for White males and perhaps Black males. Data were drawn from the first 3 waves of the 1997 National Longitudinal Surveys sponsored by the Bureau of Labor Statistics which involved a cross-sectional sample of respondents representative of all youths (6,748 youths) and an oversample of Black and Hispanic youths (2,236 Black and Hispanic youths). The final sample considered in this analysis included 7,467 youths and the variables under analysis included demographic characteristics, youth and family background, employment measures, delinquency involvement, substance use, residential characteristics, and school enrollment variables. Data analysis involved the estimation of a random-effects Poisson model with controls for youth and family background, school background, and other individual factors. Future research should focus on identifying the elements of informal employment that cause it to be detrimental for some youth. Figure, tables, notes, appendixes, references