The aim of this study was to investigate the relationship between three Eysenckian personality dimensions - psychoticism, extroversion and neuroticism - and the Internet use. A sample of 427 Turkish university students completed the Eysenck's Personality Questionnaire, an Internet survey which contained questions about interpersonal motives for Internet use and a scale for measuring the tendency for expressing one's "true" self on the Internet. The results indicated that psychoticism was the only personality dimension related to establishing new relationships and having "Internet only" friends; and extroversion was the only personality dimension that is related to maintaining long-distance relationships, and supporting daily face-to-face relationships. The results supported the idea that for some individuals, Internet can be used as social substitute for face-to-face social interactions while for some others it can be used as a tool of social extension, depending on the user's personality characteristics. Also, psychoticism and neuroticism were found to be positively associated with the expressing "true self" on the Internet, and it was shown that the relationship between psychoticism and Internet uses as social substitute is mediated by the tendency to express one's true self on the Internet. (C) 2009 Elsevier Ltd. All rights reserved.