Adherence is an important sucess indicator of patient's treatment. It is defined as the degree of patient's compliance with the doctor's recommendations. Apart from meeting the prescribed dose and the time of taking the drug, it also includes other forms of patient's behavior such as proper nutrition and physical activity, smoking cessation, regular control and vaccination, and thus considers the patient to be an active participant in the treatment process. Adherence is determined by 5 factors - socioeconomic factors, patient factors, health system factor and therapeutic factors. Adherence studies show that more than half of the patients are nonadherent. The results obtained in the adherence testing of patients at Dubrava Clinical Hospital are similar to the results of other studies. The Croatian version of the Morisky Adherence Questionnaire consisting of 8 questions was used in the study. Hospital's information system was used to collect patient data. The study included 217 patients age 21 to 87 years. The average age of patients is 63, the average number of comorbidities is 6, and the average number of prescription medications per patient is 6,6. Examined patients had a wide range of basic diagnoses classified according to ICD-10 codes. 52,07% of patients showed some form of neadherence. As the most common cause of nonadherence patients mentioned forgetfulness. Other reasons for nonadherence are intentional nonadherence, cessation of drug use due to side effects or improving the symptoms of the disease. According to the ICD-10 classification, patients from the group C - Neoplasms and D - Diseases of the blood and blood-forming organs and certain disorders, have shown the highest adherence, over 60%. The least highly adherent patients are from the group E - Endocrine, nutritional and metabolic diseases. The highest low adherence rate was observed in patients in the group of M - Diseases of the musculoskeletal system and connective tissue. Pharmacists play a very important role in improving patient adherence both within a multidisciplinary team at hospital and in public pharmacies. It is important to educate patients about their illness and therapy, as well as long-term patients follow-up, counseling on patterns of healthy lifestyle and actively promoting their adherence.