The 2-year stability of categorical and dimensional personality disorder (PD) in an older adolescent psychiatric outpatient sample was examined. One hundred and one 15-18-year-old participants were assessed using the Structured Clinical Interview for DSM Axis II Disorders (SCID-II) at baseline and 97 were re-interviewed, face-to-face, at 2 years. Of those with a categorical PD diagnosis at baseline, 74% still met criteria for a PD at follow-up, with marked gender differences (83% of females and 56% of males). Kappa for specific PDs was low for all except antisocial. Rank order and mean level dimensional stability ranged from high (antisocial, schizoid) to moderate (borderline, histrionic, schizotypal) to low (other PDs), with no decline in PD scores over the 2 years. There was no substantial influence upon stability of dimensional PD from the presence of Axis I disorder at baseline or from outpatient or inpatient treatment. However, categorical PD endured in 100% of those receiving inpatient care. The study supports that, in late teenage outpatients, the 2-year stability of the global category of PD is high and the stability of dimensionally rated PD appears to be similar to that found in young adults in a variety of settings, especially for some cluster A and B PDs. Diagnosis and early intervention appears to be justified in this age group.