Montelukast is a leukotriene receptor antagonist that is used to treat allergy and asthma. It acts as a cysteinyl leukotriene receptor antagonist that blocks the action of leukotrienes and decreases inflammation. This agent is generally well tolerated in clinical practice. Although montelukast is generally considered as a safe drug, it can cause a few adverse drug reactions. In this case study, a rare side effect of montelukast that has been reported only twice before is presented. The importance of this case report is that the youngest patient who had ecchymosis due to the use of montelukast treatment is reported.