Conclusions: Positive MRD in BM after an average of four courses of chemotherapy and before PBSCT is an unfavorable factor for stage IV NB.

Thirteen of the 20 patients with positive MRD relapsed and 1 patient died from disease (mean 25.8 months).

Another 5 patients with positive MRD, all of them relapsed (mean 17 months after PBSCT) with a significant difference between these two groups.