Objective: The aim of the present study was to examine the association between trauma and posttraumatic stress disorder (PTSD) and substance use disorders and to examine the correlates of substance use disorder plus PTSD comorbidity in the Australian general population. Method: Data were collected from a stratified sample of 10,641 participants as part of the Australian National Survey of Mental Health and Well-Being. A modified version of the Composite International Diagnostic Interview was used to determine the presence of DSM-IV anxiety, affective, and substance use disorders and ICD-10 personality disorders. Results: Substance use disorder plus PTSD was experienced by a significant minority of the Australian general population (0.5%). Among those with PTSD, the most common substance use disorder was an alcohol use disorder (24.1%), whereas among those with a substance use disorder, PTSD was most common among individuals with an opioid use disorder (33.2%). Consistent with U.S. clinical literature, individuals with substance use disorder plus PTSD experience significantly poorer physical and mental health and greater disability than those with substance use disorder alone. In contrast, individuals with PTSD alone and those with substance use disorder plus PTSD shared a remarkably similar clinical profile. Conclusions: It is important that individuals entering treatment for substance use disorder or PTSD be assessed for this comorbidity. The addition of either disorder may present complications that need to be considered for the provision of appropriate treatment. Further research is necessary to ascertain which treatments are most effective in treating comorbid substance use disorder plus PTSD.