•Development and validation of a two-factor measure of ego dissolution.•The Ego Dissolution Scale (EDS) exhibited strong psychometric properties.•Ego dissolution and dissociation are highly related yet distinct constructs. Ego dissolution (i.e., ego loss, ego disintegration, ego death, or self-loss) is a conscious state marked by a loss or diminution of one’s sense of self and a lack of first-person experience. We developed a novel, valid, and internally consistent ego dissolution scale to both (a) assess trait-like aspects of ego dissolution, which have received scant attention to date, and (b) facilitate future research in a variety of contexts (e.g., personality, psychopathology, substance use/psychedelics, contemplative practices). We determined that the 10-item Ego Dissolution Scale (EDS; Cronbach’s α = 0.80) and its identified subfactors of Ego-Loss (Cronbach’s α = 0.84) and Unity (Cronbach’s α = 0.75) were internally consistent, possessed strong convergent (e.g., depersonalization/derealization, mysticism, unusual experiences) and discriminant validity (e.g., neuroticism, social desirability). We found ego dissolution and dissociation to be empirically related yet discriminable on a statistical basis.