Drug-related problems are prevalent and cause considerable patient morbidity and in some cases death, as well as increased health care expenditures. A classification system may contribute to identify such problems, and further to resolve and prevent them.A draft classification was circulated to a panel of physicians and pharmacists and comments were requested. Consensus was achieved after two subsequent hearing rounds where the structure, content and relevance of the draft were discussed. By means of mini cases the classification was validated concerning various professionals' understanding and interpretation of the problem categories.The classification has a hierarchical structure with 6 main categories (drug choice, dosing, adverse reaction, interaction, wrong use and other) and 12 subcategories. The system is relevant for hospitals, general practices, nursing homes and pharmacies. Validation of the system revealed that a majority would assign identical categories to 9/10 cases.We propose a validated Norwegian classification system for drug-related problems. The systems may facilitate better and more systematic documentation and communication on such problems.