Background: Clinical practice guidelines recommend prophylaxis in patients with cancer receiving a colony-stimulating factor (CSF) when the risk of febrile neutropenia (FN) is high (>20%). For patients receiving chemotherapy regimens not documented as high-risk, the decision regarding CSF prophylaxis use can be challenging, because some patients may be at high risk based on a combination of the regimen and individual risk factors. Methods: A retrospective cohort design and US private health care claims data were used. Study subjects received chemotherapy regimens classified as “low” or “intermediate,” or unclassified, in terms of FN risk, and were stratified by cancer and regimen. For each subject, the first chemotherapy course, and each cycle and FN episode within the course, were identified. FN incidence proportions were estimated by the presence and number of risk factors and chronic comorbidities. Results: Across the 17 tumor/regimen combinations considered (n=160,304 in total), 74% to 98% of patients had 1 or more risk factor for FN and 41% to 89% had 2 or more. Among patients with 1 or more risk factor, FN incidence ranged from 7.2% to 29.0% across regimens, and the relative risk of FN (vs those without risk factors) ranged from 1.1 (95% CI, 0.8–1.3) to 2.2 (95% CI, 1.5–3.0). FN incidence increased in a graded and monotonic fashion with the number of risk factors and comorbidities. Conclusions: In this retrospective evaluation of patients with cancer receiving chemotherapy regimens not classified as high-risk for FN in US clinical practice, most patients had 1 or more FN risk factor and many had 2 or more. FN incidence was found to be elevated in these patients, especially those with multiple risk factors.