Previous phenotypic factor analyses suggest that C. R. Cloninger's Tridimensional Personality Questionnaire (TPQ; 1987c) assesses 4 rather than 3 temperament dimensions. The purpose of this study was to determine whether Cloninger's revised 4-factor model showed incremental validity over his original model and to investigate the convergent and discriminant validity of Cloninger's dimensions in comparison to the personality dimensions proposed by H. J. Eysenck (1981) and J. A. Gray (1970). The sample included 2,420 women and 870 men (aged 50-96) from a volunteer population-based sample of twins. Joint phenotypic factor analyses supported Cloninger's 4-dimensional temperament model. A 4-dimensional genetical factor structure was also confirmed in genetic analyses of the TPQ higher order dimensions in women. For men only 3 genetic factors were necessary to explain the genetic variance among the TPQ dimensions.