Significance: Young adults with schizophrenia, bipolar disorder and other severe mental illnesses (SMI) have high rates of smoking, but little research has evaluated predictors of cessation activity and treatment utilization in this group. Methods: We assessed attitudes, beliefs, social norms, perceived behavioral control, intention, quit attempts, treatment utilization, and cessation among 58 smokers with SMI, age 18-30, enrolled in a randomized pilot study comparing a brief interactive/motivational vs. a static/ educational computerized intervention. Subjects were assessed at baseline, post intervention, and 3-month follow-up. Results: Over follow-up, one-third of participants self-reported quit attempts. Baseline measures indicating lower breath CO, greater intention to quit, higher perceptions of stigma, psychological benefits of smoking, and symptom distress were associated with quit attempts, whereas gender, diagnosis, social support, attitudes about smoking, and use of cessation treatment were not. In the multivariate analysis, lower breath CO, higher intention to quit and symptom distress were significantly related to quit attempts. Only 5% of participants utilized verified cessation treatment during followup. Consistent with the Theory of Planned Behavior, attitudes, social norms and perceived behavioral control regarding cessation treatments correlated significantly with intention to use treatment. Norms and beliefs about treatment were somewhat positive and some improved after intervention, with a pattern