Background Asthma-COPD overlap syndrome (ACOS) has been recently described by international guidelines. A stepwise approach to diagnosis using usual features of both diseases is recommended although its clinical application is difficult. Methods To identify patients with ACOS, a cohort of well-characterized patients with COPD and up to 1 year of follow-up was analyzed. We evaluated the presence of specific characteristics associated with asthma in this COPD cohort, divided into major criteria (bronchodilator test > 400 mL and 15% and past medical history of asthma) and minor criteria (blood eosinophils > 5%, IgE > 100 IU/mL, or two separate bronchodilator tests > 200 mL and 12%). We defined ACOS by the presence of one major criterion or two minor criteria. Baseline characteristics, health status (COPD Assessment Test CAT), BMI, airflow obstruction, dyspnea, and exercise capacity (BODE) index, rate of exacerbations, and mortality up to 1 year of follow-up were compared between patients with and without criteria for ACOS. Results Of 831 patients with COPD included,125 (15%) fulfilled the criteria for ACOS, and 98.4% of them sustained these criteria after 1 year. Patients with ACOS were predominantly male (81.6%), with symptomatic mild to moderate disease (67%), who were receiving inhaled corticosteroids (63.2%). There were no significant differences in baseline characteristics, and only survival was worse in patients with non-ACOS COPD after 1 year of follow-up ( P  < .05). Conclusions The proposed ACOS criteria are present in 15% of a cohort of patients with COPD and these patients show better 1-year prognosis than clinically similar patients with COPD with no ACOS criteria. Trial Registry ClinicalTrials.gov; No.: NCT01122758 ; URL: www.clinicaltrials.gov