While several qualitative studies suggest that beliefs and attitudes are important in explaining men's alcohol-related aggression, no quantitative instrument measuring men's beliefs and attitudes about male alcohol-related aggression has been developed. The purpose of this study was to develop and test a theoretically based multidimensional inventory measuring Beliefs and Attitudes toward Male Alcohol-Related Aggression (BAMARA) consisting of 9 dimensions: (i) expected negative consequences; (ii) expected positive consequences; (iii) personal approval; (iv) perceived male peer approval; (v) perceived female peer approval; (vi) perceived normality; (vii) relaxed norms when drinking; (viii) alcohol as an excuse; and (ix) male honor/protection of masculinity. A random sample of 1,343 young adult male college and university students participated in an online survey. Item analyses using confirmatory factor analytic (CFA) and item-response theory (IRT) procedures were conducted to select a refined pool of items promoting high internal consistency and discriminant validity of the 9 scales. We evaluated the criterion validity of the 9 scales, the BAMARA total score (BAMARA-Total), and a short form of the inventory (BAMARA-SF) in terms of their association with experiences of barroom aggression and other theoretically linked constructs. CFA and IRT analyses resulted in a 53-item inventory consisting of the 9 scales with adequate model fit and good internal consistency indices. Criterion validity was demonstrated, with the BAMARA scales correlating well with reports of actual experiences of aggression in bars. BAMARA-Total and BAMARA-SF were found to be significantly associated with barroom aggression controlling for a number of important control variables. This new instrument is expected to have many important applications in the male aggression literature, with the full BAMARA being employed for the assessment of specific beliefs and attitudes and the BAMARA-SF used as a general attitudinal measure.