Inmates with serious mental illness (SMI) or antisocial personality disorder (APD) average higher rates of disciplinary infractions than inmates without these conditions. This study builds upon these lines of research by examining the relationships among SMI and various types of prison misconduct, and whether these relationships are moderated by the presence of APD. SMI was observed significantly related to annual rates of both violent and serious nonviolent misconduct. APD moderated the relationship between SMI and serious nonviolent charges but not the relationship between SMI and violent charges. Implications for inmate management and classification practices aimed at ameliorating misconduct are discussed.