We used multiple regression to calculate a new Ego Impairment Index (EII-3). The aim was to incorporate changes in the component variables and distribution of the number of responses as found in the new Rorschach Performance Assessment System, while sustaining the validity and reliability of previous EIIs. The EII-3 formula was derived from a large, diverse, developmental sample (N = 411) and was tested on an independent validation sample (N = 206) procured from psychiatric, forensic, research, and nonclinical control contexts. Additional analyses revealed high correlations with previous EIIs with similar reliability and validity but superior distributional qualities. (Contains 2 notes and 8 tables.)