Background:adherence to medication is a growing issue and there aremany factors affecting adherence in bronchial asthma and COPD. Objectives:This study was designed to determine the factors affectingadherence to inhalation therapy in asthma and chronic obstructivepulmonary disease. Patients and Methods:The present study included 300 patients (164males and 136 females and 156 COPD and 144 asthma also 189 werealready on inhaler therapy and 111 were naive(no previous inhaler)whoattended Sohag university hospital (inpatient department and outpatientclinic of chest diseases)during the period from April 2016 to May 2017using morisky questionnaire to determine factors affecting adherence toinhaled therapy. Results: 300 patients 164cases (54.67%) were males and 136 cases(45.73)were female, Good adherence to inhaled therapy was observed in 124 (35.3%) patients and both intermediate and good adherence was observed in 227 ( 64.6% ) patients. Most of the naive patients were poor adherent to inhaled therapy.There was no relationship between demographic data and adherence in asthmatic patients. However, there was significant relation between adherence and socioeconomic status and residence in COPD patients. Patients with bronchial asthma had better adherence to inhaled therapy than patients with COPD, However good adherence was frequently encountered in patients with COPD who had 2-4 emergency visits in the last year. Good adherence was observed frequently in patients who had ENT diseases as comorbidity, while poor adherence was observed frequently in patients who had cardiac disease. Good adherence was frequently encountered among asthmatic patients whoused inhaler twice daily, who used drugs its onset of action 5-20 minutes, whoused aerolizer and turbohaler devices and who used budesonide and budesonide/formetrol. Good adherence was frequently encountered among patients with COPD who used inhaler twice daily, who used aerolizer and handihaler devices and who used formetrol and tiotropium Conclusion: This study confirmed that many factors affect adherence toinhaled therapy,so the interventions to maintain adherence contain fivecategories should be joint together(patient related factors, condition related factors, drug related factors, healthcare system related and socioeconomic status)to improve adherence and thus quality of life.