The improvement in acute lymphoblastic leukemia (ALL) children treatment results in the need of examining their immune system after therapy. The purpose of the research was the immune system evaluation in children with low risk ALL diagnosis, during the treatment and twelve months after therapy. The examined material included 41 children. A group of 16 patients was examined during the above the treatment, immediately after intensive chemotherapy. The other 25 patients were examined twelve months after the completion of therapy. The lymphocyte immune phenotype was examined with FACScan flow cytometer using monoclonal antibodies. The study confirmed the intensive chemotherapy significantly decreases the number of leukocytes, lymphocytes and their subpopulations. The period of 12 months after cessation of the chemotherapy is sufficient to recover the immune system function in all examined low risk ALL children.