To our knowledge, no studies have specifically analyzed the influence of personality facets on smoking outcomes using measures of carbon monoxide (CO) in expired air at the end of treatment and at 12-month follow-up, in smokers from clinical population. According to previous research, studies about smokers from clinical population should include multiple assessments (baseline, post-treatment and follow-ups), and biochemical verification to avoid an overestimation of the absolute abstinence rate. The aim of the present study was to analyze the influence of 30 specific facets of the Five-Factor Model of personality on the short and long-term outcomes of a smoking cessation treatment.