Adherence to medication is a common problem in chronically ill patients. Three patients are presented who did not or did not fully adhere to their medication: a 3-year-old girl with asthma, a 57-year-old man with COPD and a 16-year-old boy with diabetes. This illustrates that adherence is not determined by age or illness. Known determinants of adherence are the patient's beliefs about illness and medication. Since these beliefs differ from patient to patient, dealing with non-adherence requires patient-centred care characterized by concordance, i.e. shared decision-making about therapy by doctors and patients. Appropriately targeted interventions, such as motivational interviewing, may influence patient beliefs and improve adherence.