Empathizing and systemizing have recently been put forward as two important individual-difference dimensions, whose different mean levels in men and women are argued to account for many psychological sex differences. This paper presents a series of studies designed to investigate the reliability and validity of the empathizing and systemizing quotients (EQ & SQ), to relate them to existing personality constructs, and to replicate reported sex and sexual orientation-related differences. Correlations with interests and social behaviour suggest the two measures are valid. However, empathizing appears essentially equivalent to agreeableness in the five-factor model of personality. Systemizing ...