A small number of young mentally ill persons consumes a disproportionate amount of psychiatric service resources. These persons are characterised by emotional instability, aggressive or delinquent behaviour, substance misuse and personality disorders. They are sometimes referred to as young adult chronic patients (YACP). To date there has been no investigation as to what impact this pattern of problem behaviour has on vocational rehabilitation. Aim: The aim of this study was to find out whether belonging to the YACP group, as determined by an operational definition, reduces the outcome of vocational rehabilitation. Method: A chart review was done of the files of all 174 participants of a 15-month vocational training course held between 1.1.1993 and 2.5.1998 in the vocational training centre at Cologne. A 15-item score was used to assess YACP status. Results: 30% were classified as high scorers, i.e. YACP. 59% of the high scorers vs. 22% of the low scorers terminated training prematurely. Of the high scorers who completed training, only 47 (vs. 74% of low scorers) were judged to be able to work at the end of training. Conclusion: At the very beginning of the vocational training persons in need of a highly individualised format can be discerned by a few, easy to assess items. Concepts of vocational training should be developed to better suit the needs of young mentally ill persons with personality disorders and substance abuse.