The expiration of biotech drugs patent has led to the creation of drugs copies of originator products, defined ‘biosimilars’. No European country allows automatic substitution between the originator and the biosimilar. In Italy, due to the lack of a national legislation, some Regions have issued directives to encourage the use of biosimilars, recognizing a potential saving of resources. Campania Region was the first region to legislate on the matter, (decree no. 15 of 11.30.2009) supporting the prescription of biosimilars to the naive patient. The aim of our study is to describe trends in biosimilars consumption in Campania region and evaluate how biosimilar products are replacing the originators in the respective markets. IMS Health regional database was used to analyze biosimilar drugs consumption patterns (erythropoietins, G-CSF, somatropin) in the years 2009- 2012. Information was retrieved about different distribution channels (retail, direct distribution, hospital). Consumptions are expressed in Counting Units (CU) and trends have been calculated using Compound Average Grow Rate (CAGR). The study especially focused on consumption trends of erythropoietin (ATC B03XA) in the years 2009-2012. In 2012 the penetration rate of biosimilars was 40.1% (evaluated as the biosimilars share of the total erythropoietins, G-CSF, somatropin market). These values are double than those at national level, that are estimated to be 19.7% of consumption. Focus on erythropoietin trends showed a strong increase in biosimilars consumption (451 CU in 2009 vs 140,327 CU in 2012) after the introduction of regional measures to promote the prescription of biosimilars to the naive patient. In 2012, biosimilar erythropoietins and reference drugs show similar market shares (37.0% and 33.7% of the total erythropietins market respectively) showing a high substitution effect. Our analysis outlines the significant effects of regional measures on market penetration rates of biosimilars.