Objectives: To compare the effects of resident physician motivational interviewing (MI), resident physician MI plus registered nurse (RN), and the standard of care counseling approach- ask, advise, assess, assist, and arrange follow-up (5 As)-on current smokers' behaviors (readiness to quit, cigarettes smoked per day, current smoking rates), self-efficacy to quit smoking, and nicotine dependence. Methods: The study design was quasi-experimental pretest/posttest with a comparison group. Pencil/paper measures were completed in the clinic setting at baseline and via telephone approximately 1 and 2 months after the clinic visit. Results: There were no differences among the three groups in the proportion of participants who quit smoking, and the stages of change did not differ among the groups or over time. There was a significant time effect and a decrease in the number of cigarettes smoked per day (F-2,F-160 = 41.04, P < 0.001). Significant group x time interactions were present for self-efficacy (F-4,F-140 = 8.20, P < 0.001), nicotine dependence (F-4,F-140 = 6.22, P < 0.001) and satisfactionwith clinician (F-4,F-160= 3.81, P = 0.006). Post hoc analyses showed that participants in the MI groups smoked fewer cigarettes, had higher self-efficacy, and had lower nicotine dependence scores. Only participants in the MD-plus-RN follow-up group had significant positive changes in satisfaction scores. Conclusions: Resident physicians who use MI techniques have a tremendous effect on patients' smoking behaviors. When the resident physician and the RN worked together, participants achieved better outcomes.