Successful veterinary treatment of animals requires owner adherence with a prescribed treatment plan. The aim of our study was to evaluate and compare the level of adherence of the owners of patients presented for behavioural, cardiological, urological, and oncological problems. At the end of the first examination, each owner completed a questionnaire. Then, the owners were called four times to fill out another questionnaire over the phone. With regard to the first questionnaire, statistically significant data concern behavioral medicine and cardiology. In the first area the owner's worry decreases during the follow-up and the number of owners who would give away the animal increases. In cardiology, owners who think that the pathology harms their animal's quality of life decreased significantly over time. With regard to the 9 additional follow-up questions, in behavioural medicine and urology the owner's discomfort resulting from the animal's pathology significantly decreases over time. Assessment of adherence appears to be an optimal instrument in identifying the positive factors and the difficulties encountered by owners during the application of a treatment protocol.