A major area in the study of men and masculinity concerns how the internalized masculinity ideal contributes to aggression, violence, and substance disorders. The purpose of this research was to examine the relationship among masculine gender role strain and level of aggression and severity of substance dependence in a population of incarcerated male criminal offenders. A total of 783 incarcerated, adult, male, sentenced jail inmates participated in the study. Of these, 250 men were chosen for the second level of testing based on scoring in the ± .5 standard deviation range of potential scores on at least two of three masculine gender role measures placing them at the extremes (high/low) for masculine gender role strain. These two groups were then assessed for the presence of a substance disorder at a second interview and qualified if they had a diagnosis of substance dependence on at least one class of drug. A multivariate analysis of covariance procedure (MANCOVA) evaluated masculine gender role strain for its ability to predict level of aggression and severity of substance dependence. Predictor variables were measured using (a) the Conformity to Masculine Norms Inventory, (b) the Gender Role Conflict Scale-I, and (c) the Masculine Gender Role Stress Scale. The dependent variables, substance use and aggression, were measured through (d) the Substance Use Disorders Diagnostic Schedule, and (e) the Aggression Questionnaire. Two covariates, narcissism and socially desirable responding, were assessed through the use of (f) the Margolis-Thomas Measure of Narcissism, and (g) the Balanced Inventory of Desirable Responding. Findings suggest that masculine gender role strain is useful to predict levels of aggression and severity of substance disorder in an incarcerated population (p < .001). Further, when all other predictor variables are controlled, masculine gender role ideology and desirable responding make the strongest unique contributions to predicting reports of aggression.