Purpose To describe outcomes after granulocyte colony-stimulating factor (G-CSF) prophylaxis in patients with breast cancer who received chemotherapy regimens with low-to-intermediate risk of induction of neutropenia-related hospitalization. Patients and Methods We identified 8,745 patients age ≥ 18 years from a medical and pharmacy claims database for 14 commercial US health plans. This retrospective analysis included patients with breast cancer who began first-cycle chemotherapy from 2008 to 2013 using docetaxel and cyclophosphamide (TC); docetaxel, carboplatin, and trastuzumab (TCH); or doxorubicin and cyclophosphamide (conventional-dose AC) regimens. Primary prophylaxis (PP) was defined as G-CSF administration within 5 days of beginning chemotherapy. Outcome was neutropenia, fever, or infection-related hospitalization within 21 days of initiating chemotherapy. Multivariable regressions and number-needed-to-treat analyses were used. Results A total of 4,815 patients received TC (2,849 PP; 1,966 no PP); 2,292 patients received TCH (1,444 PP; 848 no PP); and 1,638 patients received AC (857 PP; 781 no PP) regimen. PP was associated with reduced risk of neutropenia-related hospitalization for TC (2.0% PP; 7.1% no PP; adjusted odds ratio [AOR], 0.29; 95% CI, 0.22 to 0.39) and TCH (1.3% PP; 7.1% no PP; AOR, 0.19; 95% CI, 0.12 to 0.30), but not AC (4.7% PP; 3.8% no PP; AOR, 1.21; 95% CI, 0.75 to 1.93) regimens. For the TC regimen, 20 patients (95% CI, 16 to 26) would have to be treated for 21 days to avoid one neutropenia-related hospitalization; with the TCH regimen, 18 patients (95% CI, 13 to 25) would have to be treated. Conclusion Primary G-CSF prophylaxis was associated with low-to-modest benefit in lowering neutropenia-related hospitalization in patients with breast cancer who received TC and TCH regimens. Further evaluation is needed to better understand which patients benefit most from G-CSF prophylaxis in this setting.