OBJECTIVES: Although European Medicines Association approved 21 biosimilars from 2007-2014; the Food and Drug Administration approved its first, filgrastim, in 2014.  Regulatory approvals require pharmacokinetic/pharmacodynamic studies and efficacy/safety trials with fewer patients and shorter durations than for reference biologicals.  Cost savings are 20%-30%.  However, uptake of biosimilars may be delayed since clinicians and decision makers may have concerns about clinically-relevant differences in effectiveness, safety, and/or immunogenicity.  Therefore, our objective was to review published literature regarding studies of effectiveness, safety, immunogenicity, and costs of biosimilars versus reference biologicals. METHODS: We searched electronic databases using the term “biosimilar pharmaceuticals” as a major topic, with filters for English language and human species.  Our inclusion criteria were: study design for comparison of biosimilars and data included in results.  We excluded editorials, in vitro studies, and descriptive summaries. RESULTS: We identified 174 articles.  Inclusion/exclusion criteria left 19 equivalence studies for the following: epoetins (n=4, 21.1%), filgrastims (n=10, 52.6%), monoclonal antibodies (MABs) (n=2, 10.5%), tumor necrosis factor blockers and MABs (n=1, 5.3%), and interferon (n=2, 10.5%).  The median sample size was 104, but there were 3 large studies (n=6177, n=904, n=606).  Fifteen studies (79.0%) reported comparative effectiveness.  Most studies also reported on safety (n=12, 63.2%), immunogenicity (n=6, 33.6%), and/or costs (n=3, 15.8%).  Cost studies included a budget impact model regarding potential savings from adopting biosimilars versus reference biologics for rheumatic disease, a model of cost savings comparing biosimilar versus reference epoetins, and a survey of uptake and associated cost savings from various biosimilar filgrastims across European Union countries. CONCLUSIONS: Most current published data on biosimilar equivalence focus primarily on effectiveness, evaluate relatively small numbers of patients, and report minimal data on safety, immunogenicity, or cost savings.  To increase uptake, biosimilar manufacturers and regulators should consider conducting post-marketing surveillance research to provide additional data on safety, immunogenicity and costs.