PURPOSE: The N-myc amplification is one of well known poor prognostic markers in neurblastoma. Because the traditional detection method, Southern blot, is expensive, labor-intensive and time-consuming, the detection of N-myc amplification is not routinely performed in Korea. The purposes of this study are to develop polymerase chain reaction (PCR) for detecting N-myc amplification in neuroblastoma tumor tissue, and to elucidate the clinical significance of N-myc amplification. METHODS: The clinical data and paraffin embedded tumor specimen of 54 neuroblastoma cases were collected from 10 medical centers in Korea. We have developed semiquantitative method of estimating gene copy number that uses differential PCR. N-myc gene primers (RC N-myc, N-myc 7-1) are amplified together with primers from a single-copy internal control gene (beta-globin). After ethidium bromide-stained agarose gel electrophoresis, the ratio of the two PCR products, which stands for N-myc amplification, is determined. Kaplan-Meier survival analysis was performed to evaluate the prognostic significance of N-myc amplification. RESULTS: The differential PCR was very effective, less expensive, less labor-intensive, and simple detection method for N-myc amplification. The percentage of N-myc amplification was higher in the patients older than 1 year old (34.1%: 14/41), when they were compared to the patients younger than 1 year old (16.7%: 2/12). The percentage of N-myc amplification was higher in the patients who have primary tumor at adrenal gland (40.9%: 9/22) than who have primary tumor at retroperitoneum (17.6%: 3/17) or at mediastinum (16.7%: 2/12). In Stage I, II, and III patients, the mean survival time of N-myc amplified group was 18 months and that of N-myc umamplified group was 64 months (Log Rank 4.35, P=0.037). CONCLUSION: The differential PCR was very effective, less expensive, less labor-intensive, and simple detection method for N-myc amplification. The N-myc amplification is one of poor prognostic indicators in Neuroblastoma.