Aim: To compare the incidence of febrile neutropenia (FN) after same-day versus next-day pegfilgrastim. Materials & methods: This single-institution, real-world, retrospective electronic health record-based study included patients who received chemotherapy and prophylactic same-day or next-day pegfilgrastim/pegfilgrastim-cbqv. Results: In cycle 1, 117 patients received same-day pegfilgrastim and 180 patients received next-day pegfilgrastim. FN episodes in cycle 1 occurred in 6.0 versus 6.7% of patients with same-day versus next-day pegfilgrastim, respectively (p = 0.814). Across all cycles, 8.5 and 9.4% of patients experienced ≥1 FN episode after same-day versus next-day pegfilgrastim, respectively (p = 0.793). In the breast cancer patient subgroup, FN occurred 3.2% of same-day pegfilgrastim cycles versus 1.8% of next-day pegfilgrastim cycles (p = 0.938). Conclusion: No significant differences were detected between same-day and next-day pegfilgrastim administration.A common side effect of chemotherapy is the unintended killing of important immune cells that can fight infections. Because of this effect, patients with cancer who are treated with chemotherapy can experience a serious, sometimes deadly condition called febrile neutropenia (FN). Pegfilgrastim is a medication that is usually given on the day after chemotherapy to help immune cells grow and prevent FN. Many patients prefer to have pegfilgrastim administered on the same day as chemotherapy to avoid a second clinic visit, but it has not been proven whether this approach is as effective and safe as giving pegfilgrastim a day later. This study from the Utah Cancer Specialists in patients with various tumor types (e.g., breast cancer, lung cancer) showed that similar, low proportions of patients had FN when they were given pegfilgrastim on the same day as or the day after chemotherapy.