Treatment seeking substance abusers were classified as current smokers or non-smokers to identify differences between groups on psychiatric and substance use severity variables. The Addiction Severity Index (fifth edition; ASI) was administered to 313 substance abusers seeking treatment in a private, residential addictions treatment program. Since current smokers were younger and less educated than non-smokers, these variables were entered as covariates in all analyses. As measured by the ASI, current smokers experienced a significantly greater number of days with drug problems in the last 30 days and were seen as being in significantly more need of drug treatment and alcohol treatment by ASI interviewers. These findings indicate that smoking status may be a marker for greater substance use severity, although the fact that participants were not randomly assigned to groups precludes making causal interpretations of these data. Areas of future research are suggested including examining the potential mediating role of third variables such as personality and temperament.