The data for the study were taken from the National Youth Survey, a longitudinal study involving a national probability sample of youth aged 11 to 17 in 1976. The three measures of delinquency used here include index offending, minor offending, and belief or attitudes toward illegal behavior. The study distinguishes between three types of belief: strong, moderate, or weak conventional beliefs. The role of exposure to delinquent friends in the onset of illegal behavior is also considered. The study takes into account temporal priority and left-hand censoring, that is, the weakening of conventional beliefs or the onset of illegal behavior that occurred before the data were collected. The results indicate that the relationship between conventional beliefs and illegal behavior may one of mutual influence. Some weakening of belief appears to precede illegal behavior, and some illegal behavior appears to precede any substantial weakening of belief. These results are most consistent with cognitive dissonance or balance theory; reasonably consistent with control theories and with reasoned action, planned behavior, and attitude accessibility; and least consistent with self-perception theory. 3 tables, 1 figure, 4 notes, and 58 references