Biosimilars are similar, but non-identical, versions of existing biological drugs for which patents have expired. Despite the rigorous approval process for biosimilars, concerns have been expressed about the efficacy and safety of these products in clinical practice. Biosimilars of filgrastim, based on the originator product Neupogen®, have been available since 2008 and are now in widespread clinical use in Europe and elsewhere. Three biosimilar G-CSFs have been approved based on a combination of physicochemical and biological protein characterisation, pharmacokinetic and pharmacodynamic assessment in healthy volunteers and efficacy and safety data in patients with cancer. To assess whether biosimilars are effective in the real-world clinical practice setting, a pooled analysis of five post-approval studies of biosimilar G-CSF (Zarzio®) that included 1,302 adult patients who received at least one cycle of chemotherapy with G-CSF support for the prevention of neutropenia was conducted. A total of 36 % of patients had a febrile neutropenia risk of >20 %, while 39.6 % had a risk of 10-20 % based on chemotherapy regimen. The occurrence of severe or febrile neutropenia was within the range of that observed in previous studies of originator G-CSF. In addition, the safety profile of Zarzio® was consistent with that reported for originator G-CSF and the known safety profile of G-CSF. Initial concerns about the use of biosimilars, at least with regard to biosimilar G-CSFs, appear to be unfounded. Adoption of cost-effective biosimilars should help reduce healthcare costs and improve patient access to biological treatments.