OBJECTIVES: Tbo-filgrastim (TBO-FIL), a granulocyte-colony stimulating factor (G-CSF), has been available in the USA since November 2013, but approved for only one filgrastim (FIL) indication, reduction of severe neutropenia associated with myelosuppressive chemotherapy. TBO-FIL is classified as a biosimilar in Europe, but not in the USA. Our objective was to identify uptake and utilization patterns of TBO-FIL in an outpatient setting among commercially insured and Medicare supplemental populations from first entry into the US market. METHODS: Patients 18 years and older receiving G-CSF were identified in the Truven Health MarketScan® Databases between January 1, 2014 and March 31, 2014 (Q1 2014) and between April 1, 2015 and June 30, 2015 (Q2 2015). Patients were required to have a cancer diagnosis or evidence of chemotherapy during or in the 12 months prior to the calendar quarter in which they were studied. Patients were also required to have continuous enrollment during the calendar quarter of study. G-CSF use was defined as an outpatient claim for pegfilgrastim (PEG), FIL, or TBO-FIL. Demographics were measured at G-CSF receipt.  RESULTS: In Q1 2014, 11,402 patients met the study criteria (mean age 58.6 [SD=12.6], 66% female). Some received more than one G-CSF; 9,226 (81%) received PEG (75% PEG only), 2,783 (24%) received FIL (18% FIL only), and 86 (1%) received TBO-FIL (<1% FIL only). In Q2 2015, 7,958 patients met the study criteria (mean age 58.3 [SD=12.5], 66% female). Of these, 6,385 (80%) received PEG (74% PEG only), 1,784 (22%) received FIL (17% FIL only), and 304 (4%) received TBO-FIL (3% TBO-FIL only). CONCLUSIONS: The percentage of identified G-CSF patients who received TBO-FIL grew from 1% in Q1 2014 to 4% in Q2 2015, but uptake was relatively low. When data become available, future research will include filgrastim-sndz, the first US biosimilar, approved for five of six filgrastim indications.