Acute lymphoblastic leukemia is the most common form of cancer in children. The 10-year event-free survival ranged from 77 to 85% after having achieved complete remission rates of 93% or higher. The main cause of treatment failure is relapse arising from outgrowth of residual leukemic cells that are refractory to therapy. An intense effort has been made to develop methods to determine the degree of minimal residual leukemia cells present in patients considered to be in morphological remission. Because of the strong correlation between minimal residual disease (MRD) levels and risk of relapse, monitoring of MRD provides unique information regarding treatment response. The MRD monitoring based on real-time quantitative PCR detection of patient-specific immunoglobulin and T-cell receptor (Ig/TCR) gene rearrangements is currently considered to be the most reliable tool for MRD-based diagnosis in ALL. Because the significance of MRD monitoring has been strongly supported by several studies and because it has been implemented in the latest protocols, there has been a significant effort to develop MRD monitoring in the Slovak Republic since 2005. Between October 2006 and December 2009, 50 children with ALL who were treated at three Slovak centers were included in the RQ PCR MRD pilot project. A total of 40 patients with BCP-ALL ( B cell precursor ALL) and 4 patients with T ALL were analyzed for Ig/TCR rearrangement. We identified 106 different rearrangements in the 44 ALL patients analyzed. Based on MRD stratification, we identified 26 patients who were stratified into the HRG ( high risk group) (n = 3; 11.5%), IRG ( intermediate risk group) (n = 14; 54%) and SRG ) standard risk group) (n = 9; 34.5%). Morphology-based risk stratification allows the identification of most HRG patients identified also by MRD-based stratification, but fails to discriminate the IRG assigned to therapy reduction. Patients in the SRG and the IRG could profit from MRD-based risk assignment. Key words: pediatric acute lymphoblastic leukemia, minimal residual disease, immunoglobulin and T cell receptor gene rearrangements -stories of clinical oncology [1,2]. In 2000, the treatment results of childhood ALL trials performed in the early 1990s by major study groups were uniformly presented. The 10-year event-free survival ranged from 77 to 85% after having achieved complete remission rates of 93% or higher [3,4,5,6]. The main cause of treatment failure, which occurs in approximately 20% of patients, is relapse arising from outgrowth of residual leukemic cells that are refractory to therapy.Over the last 2-3 decades, an intense effort has been made to develop methods to determine the degree of residual leukemia Neoplasma 57, 6, 2010 Acute lymphoblastic leukemia (ALL) is the most common form of cancer in children, accounting for approximately 25% of all childhood cancers and about 80% of childhood leukemia. The treatment of childhood ALL is one of the true success Abbreviations: D33P -MRD positivity at day 33; D33N -MRD negativity at day 33; D78P -M...