Previous research on males, undergraduates and delinquents has shown that high mating effort is significantly correlated with delinquency, promiscuity and coercive sexual behaviour. Mating effort is defined in terms of the r/K trade-off with parental effort, such that persons at the r-end of the continuum seek to produce many offspring without great investment in their welfare, whereas the K-end of the continuum involves the production of fewer offspring and greater nurturing. A priority to gain and guard short-term mates potentially provides an evolutionary basis to offending…. Even with the highly restricted range, age correlated positively with mating effort and delinquency. Correlations were found to be of equal magnitude in both males and females. These results suggest high mating effort in both sexes is strongly related to delinquency in a normal population confirming the putative use of concepts from evolutionary psychology to understand forensic issues.