OBJECTIVES: German hospital reimbursement changed significantly as a result of the introduction of Diagnosis Related Groups (DRG) in the year 2004. Based on this development no current data on the direct costs of adverse drug reactions (ADR) leading to hospital admissions in departments of internal medicine is available. The objective of our project is to quantify the ADR-related economic burden of the respective ADRs in Germany. METHODS: A total of 1242 patient records of ADRs leading to internal medicine hospitalization were surveyed in 4 regional pharmacovigilance centres in Germany within the years 2006 and 2007. The WHO-Adverse Reaction Terminology record entries were re-coded in International Classification of Diseases (ICD-10-GM Version 2008) format and afterwards assigned to the matching DRG (G-DRG 2008) including supplementary and additional fees. RESULTS: Incidence of internal hospitalization was estimated to approximately 3.25%. Mean age of patients was 71.3 years (SD 14.5). Average inpatient length of stay in the group was 9.3 days (SD 7.0) and is therefore 2.3 days higher than average length of stay in German internal wards (7.0 days in the year 2006). Most frequent ADRs are gastrointestinal bleeding (n=205), hypoglycemia (n=201), and bradycardia (n=61). Average treatment costs of a single ADR were estimated to be approximately €2044 based on a state-wide base-rate of €2800. CONCLUSIONS: Before the introduction of the DRG system, direct medical costs of ADR-treatment in Germany were €400 million in the year 2002 (Schneeweiss et al., Eur J Clin Pharmacol 2002;58:285-91. This equals – given an ADR-incidence of 2.1% - case-related costs of € 3,700 per person. Our results provide an informative basis, that this former person-related amount seems to be too high against the background of DRG introduction. Considering the apparently higher incidence rate of 3.25%, the present total costs are approximately the same.