The psychosocial inventory of ego strengths (PIES) was devised as a measure of Erikson's eight ego strengths. The present investigation extended previous research through examination of the validity and reliability of the PIES among 502 high school students. The study also included an appraisal of Erikson's ego strengths as indices of psychosocial well-being. Reliability of the subscales of the PIES was shown through acceptable Cronbach's alphas. As expected, higher scores on ego strengths were positively correlated with psychosocial indictors of identity achievement, self-esteem, locus of control, empathic concern, perspective-taking, and positive forms of coping. Lower scores on ego strengths were related to less desirable psychosocial constructs. Biological sex and age differences also are reported. Based on the findings, the study offers validation of psychosocial theory. As well, the PIES is recommended for use among high school students.