Insulin-like growth factors (IGFs) and IGF-binding proteins (IGFBPs) have been reported to play an important role in tumor proliferation. This study aimed to investigate the validity of measuring IGF-I in the serum of children with acute lymphoblastic leukemia (ALL) as additional markers in diagnosis and follow-up of the disease. IGF-I was determined in the sera of 33 ALL patients at time of diagnosis and after an intensification phase of chemotherapy (IPC) that lasts about 6 months as well as in 21 healthy children as a control group using enzyme-linked immunosorbent assay (ELISA) technique. At time of diagnosis, serum IGF-I was significantly lower than those in the control group. After IPC, serum IGF-I returned to their normal levels. In conclusion, the changes in IGF-I could be useful to support diagnosis and follow-up of children with ALL.