Assessment and treatment of personality disorder (PD) is a key issue in UK mental health service provision (NIMH report, 2003), but there is limited information on individuals with personality disorder presenting to primary care mental health services. This study investigates the characteristics of PD in individuals receiving cognitive behaviour therapy (CBT) following GP referral and its relationship with therapist ratings of treatment process and outcome. One hundred and forty-eight participants completed the Millon Multiaxial Clinical Inventory (MCMI-III: Millon, Davis and Millon, 1997). Therapists completed a measure of therapy process and outcome (TPOQ) on 100 participants. Key therapy and process questions were answered for 60 participants who attended a minimum of five therapy sessions. MCMI-III indicated a rate of PD of 56.4%. Factor analysis of PD scales identified two factors: inward looking/emotionally distanced, and aggressive/acting out. For clinical syndromes (CLS), the factors were general psychopathology and substance abuse. TPOQ had two factors: therapeutic alliance and complexity in therapy. Regression analyses indicated that only those PDs contributing to the inward looking/emotionally distanced scale score were associated with therapeutic alliance problems. Conversely, complexity in therapy was only predicted by general psychopathology and not by personality disorder. This study identified high rates of personality disorder in primary care referrals to a clinical psychology service. It also indicated that relationships between the presence of personality disorder and therapist ratings of treatment difficulties were only associated with certain types of personality disorder. These findings are discussed in relation to service and therapy planning in mental health.