Purpose: Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a TNF superfamily member. TRAIL is transmembrane protein expressed on cell surfaces and has a broad expression pattern in a variety of organs. Cleavage of its C-terminal part (extracellular domain) allows for a soluble form of TRAIL. TRAIL induces apoptosis with its receptors TRAIL-receptor 1 (TRAIL-R1), TRAIL-receptor 2 (TRAIL-R2) however apoptosis can not be induced by receptors TRAIL-receptor 3 (TRAIL-R3) and TRAIL-receptor 4 (TRAIL-R4). There are many trials to search the correlation between leukemia and apoptotic pathway disorders. In this study we determined the seum levels of TRAIL in acute childhood leukemias at first diagnose. We aimed to determine the relation between the levels of serum TRAIL and patient's survey, clinical parameters.