This study evaluated the efficacy of using a brief motivational intervention to reduce smoking among adolescent patients treated in a hospital outpatient clinic or Emergency Department. Patients aged 14-19 years (N=85) were randomly assigned to receive either one session of motivational interviewing (MI) or standardized brief advice (BA) to quit smoking. The assessment and intervention were conducted in the medical setting proximal to the patient's medical treatment. Patients were proactively screened and recruited, and were not seeking treatment for smoking. Follow-up assessments were conducted at 1, 3, and 6 months post-intervention. Self-report data indicated that 7-day abstinence rates at 6-month follow-up were significantly higher in the MI group than in the BA group, but this difference was not confirmed biochemically. Self-reported smoking rate (average cigarettes per day) was significantly lower at 1, 3, and 6 months follow-up than it was at baseline. Cotinine levels indicated reduced smoking for both groups at 6 months, but not at 1 month. At 3-month follow-up, only those in MI showed cotinine levels that were significantly reduced compared to baseline. Findings offer some support for MI for smoking reduction among non-treatment-seeking adolescents, but overall changes in smoking were small.