Introduction: Non-adherence is common in long-term therapy for chronic diseases. Asthma and chronic obstructive pulmonary disease (COPD) are chronic diseases particularly concerned by non-adherence in Belgium as shown in previous studies about inhaled corticoids. This non-adherence has been linked to uncontrolled asthma, increased risk of asthma or COPD exacerbations and finally higher mortality. The purpose of this study was to assess medication adherence to inhaled medications in asthma and COPD for all patients in Belgium.Methods: A retrospective study using pharmacy refill data from Pharmanet- National Institute for Health and Disability Insurance was conducted. The database includes all reimbursed prescription data of all the patients from January 2013 to December 2016 about asthma and COPD medications (long acting β2-agonists - LABA, inhaled corticosteroids - ICS, anticholinergics and drug combinations) in Belgium. Medication Possession Ratio (MPR) has been used to evaluate medication adherence and patients were considered as adherent if the MPR was ≥0.8.Preliminary results: From January 2013 to December 2016 more than 23 million of asthma and COPD prescriptions have been delivered. Less than 10% of patients receiving ICS were adherent. Concerning LABA, the MPR was ≥ 0.8 for 22.1% of patients receiving salmeterol and formoterol and 60.2% for patients receiving indacaterol. About LABA+ICS combinations the proportion ranges from 12.5 (formoterol + budesonide or beclomethasone and salmeterol + fluticasone) to 65.2% (vilanterol or formoterol + fluticasone and salmeterol + budesonide). Patients seem to be more adherent to LABA + anticholinergics combinations (75% of adherent patients).Conclusion: Medication adherence is weak for ICS and LABA but tends to increase with drugs combinations. Many factors can affect medication adherence to inhaled medications as gender, age, inhaler device. These factors need further analysis in the database. Community pharmacists and general practitioners have a key role to play to ...