The aim of this study was to investigate the relationship between personality disorders, as measured by the Millon Clinical Multiaxial Inventory – III, and compliance, as measured by the Gudjonsson Compliance Scale. A voluntary sample of 58 mentally disordered offenders residing in medium secure units completed both tests. Of these, 54 (93%) met a diagnosis threshold for either a trait or a disorder (50% met the full diagnosis for at least one personality disorder). The most common personality traits/disorders were avoidant, passive-aggressive, dependent, depressive, and paranoid. The presence or prominence of clinical syndrome/severe clinical syndrome was evident in 42 (72%) of the patients. As far as clinical syndromes are concerned, the most common diagnoses were anxiety, followed by drug dependence and alcohol dependence. Compliance correlated most significantly with dependent, avoidant, passive-aggressive, and masochistic personality disorder scores (Axis II), and with dysthymia, anxiety, and delusional disorders (Axis I). These findings support the hypothesis that compliance is more strongly associated with some personality disorders than others, particularly those in Cluster C, and that the primary link with compliance is through anxiety and low self-esteem.