The Type D personality, identified by high negative affectivity paired with high social inhibition, has been associated with a number of health-related outcomes in (mainly) cardiac populations. However, despite its prevalence in the health-related literature, how this personality construct fits within existing personality theory has not been directly tested. Using a sample of 134 healthy university students, the present study examined the Type D personality in terms of two well-established personality traits; introversion and neuroticism. Construct, concurrent, and discriminant validity of this personality type was established through examination of the associations between the Type D personality and psychometrically-assessed anxiety, depression, and stress, as well as measurement of resting cardiovascular function. Results showed that while the Type D personality was easily represented using alternative measures of both introversion and neuroticism, associations with anxiety, depression, and stress were mainly accounted for by neuroticism. Conversely, however, associations with resting cardiac output were attributable to the negative affectivity-social inhibition synergy, explicit within the Type D construct.Consequently, both the construct and concurrent validity of this personality type were confirmed, with discriminant validity evident on examination of physiological indices of well-being.Keywords: Type D personality, health, neuroticism, introversion, cardiac output Type D personality, neuroticism, extraversion 3 Theories of personality have an extensive history, with the human temperament long purported to be related to physical health. Personality theories have emanated from all areas of psychology, including cognitive psychology, psychoanalysis, and social psychology. However, perhaps the most productive source has been the psychometrically driven tradition of typologies and traits. Where typological theories of personality categorise individuals into discrete types, trait theories are based on the premise that all personalities can be identified on the basis of scores within a number of traits. Classically, the trait models of Eysenck (1991) and of Costa and McCrae (1992) are among those to have received the most research interest. Eysenck's threefactor approach posits that human personality can be encapsulated in the combination of neuroticism, extraversion, and psychoticism, while Costa and McCrae's "big five" swaps psychoticism for openness, agreeableness, and conscientiousness.Recently, however, a personality type known as Type D has shown strong and lasting links to a range of negative health outcomes following coronary events (Denollet, Sys, & Brutsaert, 1995), including death (Denollet et al., 1996), second myocardial infarction (Denollet, Vaes, & Brutsaert, 2000), poor quality of life (Pedersen, Holkamp et al., 2006), and higher rates of depression and anxiety (Denollet, 1998a;Pedersen, Ong et al., 2006). While some have argued that Type D and depression overlap, studies have shown the T...