This paper describes the development of a psychometric measure of indirect aggression for use in an adult population. Items were generated from a series of qualitative interviews. Two versions of the scale were developed; the Indirect Aggression Scale Aggressor version (IAS-A) and Target version (IAS-T). Both versions of the scale were administered to separate samples (nA=294; nT=294). Scales were analysed using item analysis of internal consistency, as well as exploratory factor analysis. Both versions were found to have the same consistent three sub-scales: social exclusion, use of malicious humour, and guilt induction. Preliminary psychometric evaluation suggests that the scales are both sufficiently reliable (with Cronbach's alphas ranging from .81 to .89) and valid. There were no gender differences in either using or being the victim of indirect aggression, and the behaviour was significantly negatively correlated with age. Future validation and potential usage of the measures are discussed. Aggress. Behav. 31:1–14, 2005. © 2005 Wiley-Liss, Inc.