OBJECTIVES: Anaemia is prevalent among old individuals. Iron deficiency due to chronic gastrointestinal loss is a frequent cause. Non-steroidal anti-inflammatory drugs (NSAIDs) are a major cause of bleeding  among osteoarthritis (OA) patients. Analysis of Hospital Events Meaning IAtrogenicity (ANHEMIA) study aims at assessing the demographic characteristics of anaemia in french OA patients and its impact on hospital length of stay (LOS). METHODS: Programme de Médicalisation des Systèmes d’Information (PMSI) database covers french hospital activity and is used by Health Authorities as resources use indicators for allocating and forecasting medical budget. Its Use to assess the epidemiological and economic burden of illness is recommended. Cross-linkage through the ICD-10 diagnosis codes allowed the identification of hospital stays with a main diagnosis of osteoarthritis (OA+) and Among these, 2 subpopulations according to the existence or absence of iron-deficiency anaemia (AN+ or AN-). ICD-10 diagnosis cancers were excluded. Four groups were established for analysis: OA+AN-, OA+AN+ in either private or public hospitals (PrH, PuH). RESULTS: All the groups analysis showed a higher percentage of women (p<0.001): 2 out of every 3 patients. In PuH, mean age of OA+AN+ patients was 73.5 years vs. 65.3 for OA+AN- patients, in PrH: 69.0 years (OA+AN+) vs. 58.3 (OA+AN-). Overall, OA+AN+ patients were significantly older than 65 compared to OA+AN- patients: 88.1% vs. 68.7% (p<0.001) both in PrH or PuH.  Compared to OA+AN- patients, OA+AN+ patients had a longer LOS: 2.58 days in PuH, 2.49 days in PrH for matched DRG. The increase in LOS was accountable for substantial extra costs: €791,504 for PuH and €760,080 for PrH for the year 2006. CONCLUSIONS: Anaemia, is an important driver for extra-costs in hospitalized OA population. Since this population is likely to grow in the forthcoming years, every effort to reduce its incidence of anaemia should be considered.