Compliance with medications is one of the major issues encountered in medical practice in the treatment of many chronic diseases, as it represents the interface between the effectiveness of the drug regimen and management of the disease. Noncompliance with inhalatory therapy could be the leading cause of poor disease control and increased morbidity in conditions, such as asthma or chronic obstructive pulmonary disease. The strongest predictors of compliance are represented by the marital status, age and education of the patient, however, more research is needed in this field. Psychological factors are also known to play a role, as does the medication regimen. Assessment methods most commonly used for inhalatory therapy are self-reporting and canister weight but electronic diaries and electronic monitoring devices are more promising and reliable. Educational interventions and disease self-management plans are known to be effective in improving compliance but more specific strategies must be established. Special attention is required in children and the elderly since the compliance-related issues in these populations are more complex.