OBJECTIVES: Biosimilars of filgrastim (FIL), granulocyte colony-stimulating factor (G-CSF), have been available in Europe since 2008. Now 2 FIL products are approved in the USA: tbo-filgrastim (TBO-FIL, while a biosimilar in Europe, is not technically one in the USA; approved November 2013 for a subset of FIL indications) and filgrastim-sndz (FIL-SNDZ, the first true US biosimilar; approved March 2015, but launch delayed by ongoing litigation). Our objective was to identify physician documentation and use of TBO-FIL during patient office visits. METHODS: Physician records were extracted (1 November 2013‒18 June 2015) from RealHealthData, a US medical transcription database providing data within 72 hours of each visit to a participating provider. Records were searched for mention of TBO-FIL: “tbo-filgrastim,” “Granix,” or “Neutroval.” Mentions of FIL (“filgrastim” or “Neupogen”) and PEG (“pegfilgrastim” or “Neulasta”) were also tabulated. RESULTS: Counts of mentions (and number of unique prescribers) were as follows: PEG: 1864 (40); FIL: 431 (53); TBO-FIL: 5 (3), with >86% from oncologists in California. TBO-FIL was reported, as “Granix,” for 4 patients. Prophylactic TBO-FIL was prescribed for 1 chemotherapy patient and as interim treatment for 2 patients with chemotherapy who normally received PEG. 1 patient reported taking TBO-FIL as needed for neutropenia symptoms. Only 1 of the 4 received TBO-FIL as their main G-CSF treatment. Counts will be refreshed in October 2015 and will include FIL-SNDZ data, if launched and available. CONCLUSIONS: Among 2300 records reporting a G-CSF in this snapshot of primarily Californian oncologists, only 5 mentions of TBO-FIL were noted in the 18 months since launch. As awareness of ‘biosimilars’ improves in the USA and legal barriers are overcome, it is expected that uptake of new FIL agents will increase.  If the California data reflect national trends, uptake may continue to be slow compared with more established biosimilar markets in Europe.