Two studies were conducted among patients in a male dual diagnosis (severe mental illness [SMI] with substance use) ward. The research examined the following questions: (1) Do immigrant and non-immigrant dual diagnosis patients exhibit similar or different socio-demographic, clinical and criminological characteristics? (2) What are the implications for treatment of immigrant (and non-immigrant) patients? Study one analyzed computerized hospital records of 413 male patients; Study two examined patient files of a subgroup of 141 (70 immigrant) male patients. Alongside similarities, non-immigrant patients reported higher numbers of repeat and involuntary hospitalizations and more drug use while immigrants showed longer hospitalizations, more suicide attempts, more violent suicide attempts, more violent offenses and more alcohol use. Among non-immigrants significant relationships were found between severity of SMI and crime/violence while among immigrants a significant relationship was found between suicidality and crime/violence. Implications for treatment include need for awareness of suicide risk among immigrant dual-diagnosis patients and an understanding of the differential relationship with crime/violence for the two populations.