Objective. Pegfilgrastim is indicated to decrease the incidence of febrile neutropenia in patients with gynecologic malignancies who are receiving myelosuppressive chemotherapy. We sought to compare the safety and efficacy of day 1 pegfilgrastim administration to day 2 administration in patients with gynecologic malignancies. Methods. We retrospectively evaluated patients receiving both chemotherapy and pegfilgrastim from June 1, 2,006 to August 31, 2007 for a gynecologic malignancy. Abstracted data included patient demographics, pathology, blood Counts, toxicity, and chemotherapy, After administration of chemotherapy, all patients either received 6 ring of pegfilgrastim subcutaneously on day 1 or day 2. Results. 1226 administrations of pegfilgrastim in 230 patients were identified. 490 administrations of pegfilgrastim were given on day 1 compared to 736 on day 2. 70% of patients had ovarian cancer with a median age of 64 years (range 15-88). 79% of patients had stage III, IV, or recurrent disease and 67% were undergoing primary chemotherapy, The most common chemotherapy was docetaxel/carboplatin (53%) followed by paclitaxel/carboplatin (19%). The mean absolute neutrophil count (ANC) nadir was 4810/mm(3) in the day 1 cohort compared to 4212/mm(3) in the day 2 cohort (p=.004). The incidence of Grade 3/4 neutropenia was similar in both groups (4.9% in day 1 vs. 5.7% in day 2; p=.63). Grade 314 febrile neutropenia was uncommon in both cohorts (0 episodes vs. 3 episodes; p=.41). Treatment delays were similar in both cohorts (5.9% vs. 7.5%.; p=.35). Dose modifications were also similar in both cohorts (2.8%. vs. 5.3% p=.06). Conclusion. Day 1 administration of pegfilgrastim is as effective as day 2 administration in the prevention Of neutropenia in patients with gynecologic malignancies. Treatment delays and dose modifications were not increased after day 1 administration of pegfilgrastim. Administering pegfilgrastim on day 1 appears to be safe. effective, and convenient in selected patients receiving myelosuppressive chemotherapy for gynecologic malignancies. (C) 2008 Elsevier Inc. All rights reserved.