Background: In 2015, filgrastim, a granulocyte colony stimulating factor (GCSF), became the first biologic to have an FDA-approved biosimilar introduced in the US. One additional filgrastim and two pegfilgrastim biosimilars have since been approved. Objective: To evaluate patient characteristics and treatment use patterns in patients treated with GCSFs. This analysis will help inform a large-scale, real-world, observational GCSF comparative effectiveness research (CER) study using the Biologics & Biosimilars Collective Intelligence Consortium (BBCIC) distributed research network (DRN). Methods: Adults treated with any GCSF from 1/1/2012 to 3/31/2019 were included. A distributed query using existing FDA Sentinel System analytic tools was developed to capture characteristics of patients receiving GCSFs based on health insurance medical and pharmacy claims data. Data were aggregated from five health plan research partners in the BBCIC DRN. Results: Over 38 million eligible health plan members representing over 88 million person-years of data were evaluated; 31,023 filgrastim, 5,325 tbo-filgrastim, and 6,305 filgrastim-sndz incident users were identified. Patients were similar across groups in age (59.8 years for filgrastim, 60.5 for tbo-filgrastim, 59.8 for filgrastim-sndz) and sex, (females accounted for 58.2% filgrastim, 58.5% tbo-filgrastim, and 61.1% filgrastim-sndz). Total use of all filgrastim products remained consistent at about 6,500 incident users annually; however, filgrastim represented about one-third of all incident users by the end of the study period, with filgrastim-sndz and tbo-filgrastim making up the difference. Filgrastim products have consistently accounted for approximately 34% of incident use compared to pegfilgrastim. The first utilization of filgrastim-aafi and pegfilgrastim-jmdb was observed in 2019, but there was insufficient utilization to be included at the time of this analysis. There are no data for pegfilgrastim-cbgv to date. Conclusions: This systematic, longitudinal surveillance of GCSF utilization patterns in the US showed that new users of biosimilars increased over time while the overall number of new users remained flat. In 2018, filgrastim-sndz use accounted for the largest number of incident GCSF users. This analysis suggests availability of adequate sample size and similar patient populations to conduct a CER study in GCSFs in the BBCIC DRN.