Individuals with schizophrenia and severe mental illness smoke cigarettes at rates that well exceed the general population. Little is known about the correlates and sequelae of increased smoking severity on persons with severe mental illness. A total of 304 smokers from six community mental health centers were assessed for smoking history, psychiatric symptoms, co-occurring disorders, subjective quality of life, and expired carbon monoxide (CO). Statistical analyses identified correlates of smoking severity, as assessed by number of cigarettes smoked per week. The average number of cigarettes smoked per week was 136+/-83. Increased smoking was associated with higher levels of expired CO and being Caucasian, and with a greater likelihood of a current diagnosis of hypertension and oral/gum disease. Greater smoking severity was also associated with greater perceived stress, poorer overall subjective quality of life, and lower satisfaction with finances, health, leisure activities, and social relationships. This study confirms high rates of heavy smoking among persons with severe mental illness. The association of increased quantity of cigarettes smoked with being Caucasian is consistent with previous reports in mentally ill and non-mentally ill populations. The linkage of heavy smoking with poorer quality of life and co-occurring medical disorders suggests the importance of smoking reduction and cessation strategies to reduce smoking and decrease patients' total pack years of smoking.