A new semi-quantitative scoring system is proposed, especially designed for the comparative interpretation of sequential whole-body meta-iodo-benzyl-guanidine (MIBG) scans in stage IV neuroblastoma children. This method was applied to assess whether MIBG scan at mid-course of induction chemotherapy could predict the final response. 27 newly diagnosed children were investigated by three sequential 123I-MIBG scans performed at the beginning, at mid-course (6 weeks) and at the end of neoadjuvant chemotherapy (12 weeks). Whole body scans were divided into nine regions in which the extension of bone metastases was separately quoted (score range: 0-3). The overall absolute scores were obtained by adding the scores of the nine regions. Relative scores were calculated by dividing the absolute score at each time by the corresponding pretreatment score. The score at mid-induction correctly predicted the overall response of metastases at the end of induction (P < 0.0001) in most cases. This method is easy to use, reproducible, subject to little inter-investigator variation, and thus well adapted to multicentric trials.