Hairy cells are abnormal white blood cells with hair-like projections of cytoplasm, they can be seen by examining a blood smear or bone marrow biopsy specimen. The blood film examination is done by staining the blood cells with Wright's stain and looking at them under a microscope. Clinical Significance Hairy cells are visible in 85% cases of Hairy Cell Leukemia. Hairy cell leukemia is an uncommon haematological malignancy characterized by an accumulation of abnormal B lymphocytes ( ~2% of all leukemias). The "hairy cells" (malignant B lymphocytes) accumulate in the bone marrow, leading to pancytopenia and splenomegaly. Diagnosis ? CBC with peripheral smear showing Hairy cells ? Bone marrow biopsy with TRAP staining ? Flowcytometry – blood / bone marrow - The hairy cells are larger than normal and positive for CD19, CD20, CD22, CD11c, CD25, CD103, and FMC7 (CD103, CD22, and CD11c are strongly expressed. We express our sincere gratitude to Dr. Arpita Roy Dam for her contribution in this.