A 34-year-old man was referred to our hospital for leukocytosis and fundal hemorrhage. Peripheral blood and coagulation tests showed increases in cells at all stages of the neutrophilic series and a low level of fibrinogen (Fbg). Chronic myelogenous leukemia (CML) was diagnosed, and nilotinib was administered. During the clinical course of CML treatment, plasma Fbg levels continued to be low, but the patient showed neither hemorrhagic nor thrombotic complications. Fbg analysis showed normal antigen levels and low activity levels, which indicated dysfibrinogenemia. Genetic analysis revealed a heterozygous gene mutation (γ308AAT→AAG), a mutation which was also found in the patient's mother. Asymptomatic patients with dysfibrinogenemia have a low risk of hemorrhage in daily life and do not require treatment. However, in those undergoing major surgery or in serious accidents, replacement therapy may be required. When the cause of low Fbg levels is unknown, dysfibrinogenemia or fibrinogen deficiency should be considered. Even asymptomatic patients may benefit from more detailed immunologic and genetic analyses.