Filgrastim is a granulocyte colony-stimulating factor commonly used in the prophylaxis and treatment of neutropenia associated with chemotherapy in cancer patients. It is a well-tolerated and safe drug but some unusual serious adverse effects may occur. We expose a case of a 37-year-old woman who was hospitalized with severe pancitopenia after the first cycle of chemotherapy with a cisplatin doublet and bevacizumab. Filgrastim was administered for 3 days with the aim of increasing neutrophils and not delay the next chemotherapy cycle. Due to acute respiratory failure she was transferred to the Intensive Care Unit for symptomatic control where required oxygen therapy. Fungal and bacterial culture were made and so blood serologies, all of them were negative. It was diagnosed as pneumonitis secondary to a probable side effect of filgrastim. Although the case was resolved properly it is important monitor the administration of filgrastim because of the severity of these events.