OBJECTIVES:  The rising costs of cancer care have caused concerns regarding the increasing OOP burden on cancer patients. The objective of this study is to examine patients’ OOP expenditures on G-CSF, pegfilgrastim and filgrastim, two supportive-care agents for cancer patients treated with myelosuppressive chemotherapy.  METHODS: Two large US health care claims databases (2008-Q2 2010 MarketScan® Commercial and Medicare Supplemental Databases, and 2007-Q2 2009 HealthCore Integrated Research DatabaseSM) were used to identify adult patients receiving chemotherapy and G-CSF in outpatient settings.  The summary statistics of quarterly OOP costs were tabulated for patients with any G-CSF claim for each quarter during Q1 2007-Q2 2010. Costs were adjusted to June 2010 dollars. RESULTS: The pattern of patients’ OOP costs for G-CSF was generally consistent between the two data sources and over time. On average, about 65-75% of patients on G-CSF incurred zero OOP costs in a quarter. Across the years, the average quarterly OOP costs per patient for all patients ranged from $100-$150 for pegfilgrastim and $50-$100 for filgrastim. When focusing on the 20,948 patients on G-CSF with continuous health plan enrollment throughout 2009 in MarketScan®, mean OOP costs/patient/quarter were $100 for pegfilgrastim and $53 for filgrastim. On average 69.2% of pegfilgrastim patients and 63.9% of filgrastim patients had zero OOP costs in a quarter. Very few patients (5.5% of pegfilgrastim and 2.7% of filgrastim) had quarterly OOP costs reaching $500 or above. The subgroup of patients with >$0 quarterly OOP costs had mean costs/patient/quarter that were $324 for pegfilgrastim and $146 for filgrastim. During 2009, that subgroup had an average of 2.4 administrations and/or prescriptions per quarter for pegfilgrastim and 5.5 for filgrastim. The mean OOP costs of those administrations and/or prescriptions were $128 for pegfilgrastim and $30 for filgrastim. CONCLUSIONS:  During 2007-2010, the majority of patients did not pay OOP for G-CSF.