Some people can assume behaviors considered inhuman and brutal, such as making sexual violence on adults or even on children. Sex offenders use the other as an object that can give them pleasure, sometimes with sadistic attitude, careless of causing them suffering and shocks. Though it seems impossible, actually it happens, opening a debate on how much these persons can realize the pain they are causing, and haw can they tolerate it. In the study we present, a population of sex offenders convicted in a prison of Genoa will be tested with validated instruments to investigate some aspects of their personality, such as empathy and emotional cognition. Their ability in recognizing non verbal communication of feelings will be evaluated, in order to correlate those aspects to impulsivity, interpersonal reactivity and aggressivness, trying to understand the incomprehensible.