The present paper reviews studies investigating the possible correlation between testosterone and aggression. First, methodological considerations in testosterone research are outlined. These considerations are used as a basis on which past studies are reviewed How testosterone is related to various personality dimensions is then discussed concluding with how testosterone is related to aggression in non-criminal and criminal samples. The paper concludes with the suggestion that testosterone may have a relationship with sexually dimorphic behaviors, in particular aggression. (C) 1999 Elsevier Science Ltd All rights reserved.