Psychiatric hospitals are increasingly adopting smoke-free policies. Tobacco use is common among persons with mental illness, and nicotine withdrawal (NW), which includes symptoms of depression, anxiety, anger/irritability, and sleep disturbance, may confound psychiatric assessment and treatment in the inpatient setting. This study aimed to characterize NW and correlates of NW severity in a sample of smokers hospitalized for treatment of mental illness in California. Participants (N=754) were enrolled between 2009 and 2013, and averaged 17 (SD=10) cigarettes/day prior to hospitalization. Though most (70%) received nicotine replacement therapy (NRT) during hospitalization, a majority (65%) reported experiencing moderate to severe NW. In a general linear regression model, NW symptoms were more severe for women, African American patients, and polysubstance abusers. Though invariant by psychiatric diagnostic category, greater NW was associated with more severe overall psychopathology and greater cigarette dependence. The full model explained 46% of the total variation in NW symptom severity (F [19, 470]=23.03 p<0.001). A minority of participants (13%) refused NRT during hospitalization. Those who refused NRT reported milder cigarette dependence and stated no prior use of NRT. Among smokers hospitalized for mental illness, NW severity appears multidetermined, related to cigarette dependence, demographic variables, psychiatric symptom severity, and other substance use. Assessment and treatment of NW in the psychiatric hospital is clinically warranted and with extra attention to groups that may be more vulnerable or naïve to cessation pharmacotherapy.