OBJECTIVES: To assess the clinical consequences of primary prophylaxis (PP) with pegfilgrastim versus 6‑ or 11‑day filgrastim (F6, F11) in the prevention of febrile neutropenia (FN) in non-Hodgkin lymphoma (NHL) patients receiving CHOP‑14 chemotherapy and in breast cancer (BC) patients receiving TAC chemotherapy in Germany. METHODS: A lifetime Markov model was developed, consisting of two phases: 1) on‑chemotherapy phase (OCP), where model cycle length equals chemotherapy cycle length (CHOP-14:14 days, TAC: 21 days), and 2) post‑chemotherapy phase (PCP) with annual model cycles.  PP is defined as prophylaxis initiated with the first chemotherapy cycle. Cycle 1 FN risk with no prophylaxis (NP) was estimated to be 21% for NHL CHOP-14 and 14% for BC TAC. All cycle relative risk of FN using PP with pegfilgrastim versus no PP, F6, and F11 was 0.25, 0.87 and 0.61. FN case fatality was estimated (NHL: 8.9%; BC: 3.6%).  In PCP, all-cause mortality was estimated from German life-tables; NHL and BC mortality from US data; patients experiencing FN were assumed to have higher mortality due to reduced chemotherapy dose intensity. All inputs were estimated from clinical trials and published literature. The model estimates life-years, number of FNs, and number needed to treat (NNT) to prevent an FN. RESULTS: NNT to prevent an FN were 1.3, 6.2, 2.2 in NHL; 2.3, 11.1, 4.0 in BC for Pegfilgrastim, F6, and F11 compare to NP. Overall FN episodes per patient were 0.15, 0.76, and 0.47 in NHL; 0.09, 0.43, and 0.27 in BC.  Per-patient life-months gained using PP with Pegfilgrastim were 3.4 and 1.8 versus F6 and F11, respectively in NHL, and 2.2 and 1.2 in BC. CONCLUSIONS: Primary Prophylaxis with Pegfilgrastim results in a lower NNT, fewer FN events and more life-years than with 6-day filgrastim or 11-day filgrastim in both NHL and BC.