OBJECTIVES: Primary (first and subsequent cycles) prophylaxis with filgrastim or pegfilgrastim has been recommended in 2006 clinical guidelines when the risk of febrile neutropenia (FN) is about 20%. Recent studies reported significantly greater reduction of FN with pegfilgrastim. In clinical practice, filgrastim has often been used for fewer than the recommended 11 days (e.g., 5-6 days), which has been shown to compromise the clinical outcomes. The study purpose was to evaluate the cost-effectiveness of pegfilgrastim vs. filgrastim (11- or 6-day) primary prophylaxis in women with breast cancer (stage I-III) receiving chemotherapy with moderate to high FN risk in Germany. METHODS: We constructed a decision-analytic model from a health care payer's perspective. Costs included drugs, drug administration, FN-related hospitalizations and subsequent costs, and were based on Rote Liste (list price) and DRG Tariff. Effectiveness was measured as FN avoided and life-year-gained (LYG). FN risk(varied by days of filgrastim), FN case-fatality, relative dose intensity (RDI), and the impact of RDI on survival were based on a comprehensive literature review and expert panel validation. Breast cancer mortality and all-cause mortality were from official statistics. Sensitivity analyses were conducted on key variables. RESULTS: Pegfilgrastim use avoided more FN events, produced greater LYG and was less expensive than 11-day filgrastim. Compared with 6-day filgrastim, pegfilgrastim avoided 10.5 absolute percentage point of FN (17.5% vs. 7%) at a modest cost increase (€1,306); the incremental cost-effectiveness ratio (ICER) was €12,429 per FN avoided. The average life expectancy was 15.99 years with pegfilgrastim and 15.88 years with filgrastim, yielding an ICER of €11,972/LYG. Age of diagnosis and cancer stage had minimal impact on the results. Drug costs and FN risk has moderate influence on model results. CONCLUSIONS: In Germany, pegfilgrastim appeared to dominate 11-day filgrastim and to be cost-effective within normal thresholds compared with 6-days filgrastim per cycle.