['Chronic obstructive pulmonary disease (COPD) is associated with poor prognosis and a high health care burden. The incidence of asthma and COPD overlap syndrome is increasing, and contributes to a high financial burden and poor prognosis.', 'To investigate clinical features of the overlap syndrome among Asian patients and to analyse its impact on hospitalisation due to respiratory problems or death compared to COPD alone.', 'We performed a retrospective cohort analysis of 2933 COPD patients presenting at the Asan Medical Center from 1 January 2000 to 31 December 2009. Kaplan-Meier and Cox proportional hazard models were used to analyse the significance of clinical parameters, including age, sex, smoking history, body mass index (BMI), severity of airflow limitation, airway obstruction reversibility and overlap syndrome with hospitalisation due to respiratory problems or death.', 'Overlap syndrome patients were older, included smaller proportions of males and of smokers and had lower forced expiratory volume in 1 s (FEV1) (% predicted). Shorter hospitalisation-free and survival periods were noted among overlap syndrome patients. Overlap syndrome was significantly associated with risk of hospitalisation due to respiratory problems after adjusting for age, smoking history, BMI, FEV1 (% predicted) and changes in FEV1 (P < 0.001).'] Do asthma and COPD overlap syndrome is associated with increased risk of hospitalisation?