The current study examined whether delinquents' general aptitude test scores would predict attrition in a vocational preparation focused programme. Results showed that completers and noncompleters were significantly differentiated on general learning ability, verbal, numerical and spatial aptitudes, with completers displaying higher levels of functioning. Numerical and, to a lesser degree, spatial aptitudes emerged as the best discriminators between the two groups. The derived discriminant function produced a correct prediction ('hit') rate of 71 percent, accurately predicting almost all of the noncompleters (13 out of 15). However, it misclassified 10 of the 26 completers. In view of this tendency to overpredict the number of noncompleters, low aptitude scores alone appear to be limited in their usefulness to predict attrition in individual youths. It is suggested that future research should examine whether aptitude interacting with other factors can differentially influence the probability of attrition. (Author abstract)