Background and aim: Drug-related problems (DRP) jeopardize patient safety. Unit-dose dispensing systems (UDDS) with computerized-physician-order-entry (CPOE) and clinical-decision-support-systems (CDSS) were reported as a promising concept for preventing DRP. We aimed at identifying and categorizing DRP in peroral drug administration considering their clinical risk and preventability by UDSS/CPOE/CDSS. Investigations: In surgical and internal-medicine departments, we observed routine procedures in peroral drug administration for DRP. An expert panel including pharmaceutical and nursing expertise categorized the identified 18 DRP categories into three levels: DRP that have not yet resulted in medication errors (ME) (Level-I), DRP where ME have occurred but have not yet reached the patient (Level-II), and DRP where ME have occurred and have reached the patient (Level-III). Additionally, the panel categorized DRP according to their clinical risk and whether the implementation of UDSS/CPOE/CDSS can prevent them. Results: In 77 surgical patients, 1,849 peroral drug administration procedures, and in 149 internal-medicine patients, 1,405 procedures were observed. The 18 DRP categories were identified with a frequency of 0.6%-26.7% (Level-I), 0.1%-21.5% (Level-II), and 0.0%-1.0% (Level-III). Of those, four categories were considered of high clinical risk: "Name of the medication is not readable", "Prescribed medication is not prepared for administration", "An incorrect or non-prescribed medication is prepared", and "A medication is prepared for the wrong patient (mix-up)". Twelve DRP categories were categorized as highly preventable by UDSS/CPOE/CDSS. Conclusions:Under routine conditions, we identified a substantial number of DRPs. An expert panel categorized many of those DRPs as clinically highly relevant and highly preventable by UDSS/CPOE/CDSS.