Leukocytosis is defined as having a leukocyte count over 10.000/mm3 in adults. Showing a progressive increase during pregnancy, peripheral leukocyte count may rise up to 20.000-30.000/mm3 at birth. A 32-year-old G2P1 patient whose leukocytosis continues for about 15 years, was referred to our hospital due to a WBC of 35.000/mm3 at gestational week 30. We found out that the patient's mean preconceptional WBC had been 15.000/mm3 and her mean WBC went up to 20.000/mm3 at early pregnancy. The patient was diagnosed with idiopathic leukocytosis by haematology department and LMWH Clexane 0.4 1x1 (Enoxaparin 0.4 ml, Sanofi- Aventis) was given subcutaneously during the course of pregnancy. Her WBC was 16.300/mm3 at postpartum day 10. The patient's WBC was 12.000/mm3 at postpartum week 6 (after using LMWH) and 14.800/mm3 at postpartum week 8. We think that when the results of the two pregnancies are examined in this rarely seen case and chronic idiopathic leukocytosis is monitored together with LMWH, the potential negative effects on maternal, fetal, and neonatal outcomes (due to predisposition to thrombotic process) can be diminished.