Tumors of histiocytes are among the rarest of tumor affecting lymphoid tissues. As these tumor types were poorly recognized until recently, it is sometimes difficult to establish diagnosis and their clinicopathological features are still obscure. Here, we report a case of hitiocytic/dendritic neoplasm with marked blood coagulation disorder. A 71-year-old woman was admitted to the hospital for progressive abdominal distention and bilateral cervical lymphadenopathy lasting for a month. Computed tomography scan showed marked hepatosplenomegary and ascites and low gastrointestinal endoscopy showed ileal neoplasm. Pathological findings of the tumor showed proliferation of large pleomorphic cells with abundant and eosinophilic cytoplasm and infiltration with small T-lymphocytes. She was suspected with malignant lymphoma and transferred to our hospital after one week from her first hospitalization. On admission, her performance status was 3 and she showed systemic subcutaneous bleeding and marked abdominal distention. Her laboratory data showed marked blood coagulation disorder (Plt 2.6 × 103/m3, PT INR 1.74, APTT 51.1 s, Fib 60 mg/dl, AT III 14%, FDP-s 2.8 μg/ml, PIC <0.3, TAT 31.4 ng/ml) and liver dysfunction (T-Bil 3.1 mg/dl, LDH 528 U/l, AST 98 U/l, ALT 685 U/l, ALP 685 U/l). We had to abandon lymph node biopsy for definitive pathological diagnosis because of her severe coagulopathy but bone marrow aspirate examination revealed 14% of large abnormal cells resembling ileal tumor cells which were positive only with CD4, CD11c, CD103, HLA-DR and negative with other lymphoid markers. B- and T-cell histiocytic lineage markers excepting CD4 of iliac tumor were also absent but S-100 protein was positive. Her disease was distinguished from malignant lymphoma and diagnosed as hitiocytic/dendritic neoplasm. She wanted to keep palliative care and passed away at three weeks after her first hospitalization.