There are only few publications about patient compliance in in-patients. The compliance of 134 female patients of a common hospital was detected after prescription of riboflavin tablets. Over a period of 10 days four examinations of the urine for signs of fluorescence were performed. 24% of the in-patients were noncompliant. Patients aged over 70 years or with chronic diseases like diabetes or hypertension were seen to have a good compliance compared with younger ones or patients without these diseases. In-patients with psychiatric or psychosomatic disorders were more incompliant than the other ones. In this group the intake must be controlled. A large number of prescribed tablets negatively influenced the compliance but the frequency of intake did not adversely affect the compliance. The history of individual patient compliance will indicate the future compliance. The results show that compliance should be taken into account in in-patients care especially according to a successful therapy.