Tumors of the sympathetic nervous system (NT), namely neuroblastoma (NB) and ganglioneuroblastoma (GNB), have a variable clinical course. Prognostic factors include clinical stage, age of the patient, histological grade, and changes at the genomic level, of which amplification of N-myc oncogene is a well recognized phenomenon. The aim of this study was to establish the status of the N-myc oncogene in NT and to compare the results with histopathological grading, with risk groups according to criteria outlined by Joshi et al., and with the clinical stage. To detect the amplification of N-myc oncogene we used differential polymerase chain reaction (D-PCR). Amplified N-myc oncogene was found in 10 out of 31 investigated children with NB (32%). The result of D-PCR could not be interpreted reliably in two patients. Of seven children with GNB the N-myc amplification was found in one case. None of seven children with ganglioneuroma was found to have amplified N-myc oncogene. The tumors with N-myc amplification were histologically poorly differentiated of undifferentiated with a high mitotic activity-8 children were classified as a high risk category; in two we had not enough surgical material to evaluate the histological prognostic factors. The correlation of N-myc status with clinical stage revealed N-myc amplification in two of 9 children classified as clinical stage III, and in eight of 11 children classified as clinical stage IV. The N-myc amplification was not found in any child diagnosed at stage I, II and IV. Five of 10 children with NB and N-myc amplification died of the disease progression. Four children died in the group of 19 children without N-myc amplification. The median of follow-up was 18 months. The patient with GNB and N-myc amplification also died of the disease progression. Although the follow-up period of the investigated group of patients was short, the results showed that the amplification of N-myc oncogene was associated with tumors of patients diagnosed at a late clinical stage (III and IV), and with tumors whose morphology and age were assessed collectively under the term "high risk group".