This study compares the severity of DSM-III-R psychoactive substance use disorders (PSUDs) among dually diagnosed psychiatric inpatients with independent axis I mental disorders (IMDs) with the severity of PSUDs among: a) patients from the same hospitals with PSUD-related organic mental syndromes (PSUD-OMD) and b) patients from a residential drug-treatment program with PSUDs but no axis I mental disorders. The drug-use disorders among the group 1 (IMD+PSUD) patients were less severe on multiple indicators from the Structured Clinical Interview for DSM-III-R (SCID) and the Addiction Severity Index compared with the drug-use disorders among the other two groups. This did not hold for alcohol disorders. These findings carry potential implications for treatment strategies for the mentally ill with drug use.