A four stage regressive model that links public stigma to self-stigma is applied to mental illness and substance use disorder. We assess this four stage model in those with co-occurring disorders versus those who have mental illness or substance use disorder alone.366 people who self-identified as having either a mental illness or co-occurring mental illness with substance use disorder were recruited from MTurk and completed measures on identity and self-stigma.Higher group identity predicted lower selfstigma in those with mental illness while this effect was not present for participants with co-occurring disorders. Limitations include that this study only looked at mental illness identity for those with both mental illness and substance use disorder; sample limitations are also discussed.Those with co-occurring disorders may identify more with certain groups over others.