Background: Primary G-CSF prophylaxis after chemotherapy is recommended in evidence based guidelines (GL), if the risk of febrile neutropenia (FN) is high (≥20%), or intermediate (≥ 10% - 20%) in case of risk factors. The aim was to evaluate, if G-CSF is used as proposed by GL, to identify determinants of GL implementation and adherence. Methods: The sample size was calculated at 2% of the incidence of malignant lymphoma, breast and lung cancer in Germany. Pts who had received 3-9 cycles of chemotherapy with a FN risk ≥10% between 5/2011 to 4/2012 were documented retrospectively. Results: 286 lymphoma, 666 lung cancer and 976 breast cancer pts were collected from 87 hospitals and 59 oncology practices with 195 physicians participating. Adherence to GL was higher in physicians up to 10 than over 10 years of experience. Conclusions: The adherence to and acceptance of GL for G-CSF may not be sufficient. Patient risk factors are underestimated therefore resulting in a possible underuse of G-CSF. Physicians may underestimate FN risk in pts who have an intermediate risk of FN and they overestimate their adherence to the GL.