Background: Although granulocyte colony stimulating factor (G-CSF) mobilization is generally well tolerated by healthy donors, there is also a wide spectrum of adverse events associated with it. Among these events, rhabdomyolysis in peripheral blood stem cell (PBSC) donors is very rare. In this paper, we present a first case of rhabdomyolysis after administration of filgrastim for PBSC mobilization. Case Report: A 6-year-old donor received 10 mu g/kg/day filgrastim subcutaneously for 5 days. On the 3rd day of filgrastim, the donor complained of bone pain; a single dose of paracetamol (250 mg) was given to relieve pain. On the 4th day, she complained of bone pain, myalgia, and vomiting. On laboratory analysis, serum creatine phosphokinase was 1,095 U/l (40-226 U/l), LDH 312 U/l (100-190 U/l), aspartate aminotransferase 85 U/l (0-40 U/l), potassium 3.3 mmol/l (3.6-5.1 mmol/l). Urine myoglobin was 110 ng/ml (< 5 ng/ml). Rhabdomyolysis was suspected on clinical and laboratory findings. Clinical manifestations regressed and the laboratory results returned to normal within three days after intravenously forced diuresis and potassium replacement. Stem cells were successfully harvested from peripheral blood on the 5th day of G-CSF therapy. Conclusion: Rhabdomyolysis is a rare but important adverse effect of G-CSF. Allogeneic PBSC donors should be closely monitored with regard to rhabdomyolysis after G-CSF administration in the mobilization setting.