Adolescent smoking is a major public health problem, which has led to the development of cessation programs such as Project EX. However, there is no evidence for the long-term efficacy of cessation among Spanish adolescents. This study provides a 1-year follow-up evaluation of the Project EX tobacco use cessation program among 211 smokers. The intent-to-treat 30-day smoking quit rate for the program group was 7.81 percent (p = .04), whereas no smokers quit in the control group (p = .02). The intervention had a significant influence on future smoking expectation, intention, motivation to quit, and overall level of 30-day smoking. Long-term outcomes of the Project EX clinic-based program are promising for adolescent smokers in Spain.