A leukemoid reaction is an extreme form of reactive leukocytosis defined as granulocytic leukocytosis above 50 × 10(9)/L produced by normal bone marrow, mostly in response to systemic infection or cancer. The mechanism as to how the haematopoetic system is altered to elevate production of myeloid cells is not known. A 69-year-old man presented with phlegmasia cerulea dolens caused by massive iliofemoral thrombosis. His workout at admission revealed absolute white blood cell count of 73.4 × 10(9)/L, with neutrophil granulocyte of 68.5 × 10(9)/L. The new increase in white blood cell count happened at day 5 after admission, when the haematoma of the anteromedial thigh was evacuated in general anaesthesia. There was a gradual decrease in counts until they reached the normal range. Deteriorated general condition with signs of systemic inflammatory response syndrome improved with supportive therapy, and the patient was discharged from hospital after 30 days. During hospitalization we did not identify any infectious focus, or any malignancy. We could not exclude other occult chronic conditions (malignancy) but the patient did not develop any other condition during 4.5 years of follow-up.