Bone marrow biopsy is very important in diagnosis and follow-up of children affected by neuroblastoma (NB). Between June 1995 and May 1997 we studied 55 patients with NB stage 4. Specimens were obtained at the diagnosis (in 8 patients) and after chemotherapy (in 55 patients) in order to evaluate the effects of treatment on bone marrow disease. 88% of 343 biopsies were representative versus 99% of 639 aspirates. Of 8 stage 4 patients evaluated at diagnosis, 15/16 biopsies versus 9/15 aspirates were positive. Following chemotherapy, out of 298 evaluable sites examined, 111 biopsies versus 30 aspirates (37 versus 10%) were positive. Of 111 positive biopsies 53 showed a focal pattern (35 differentiated, 18 undifferentiated), while 51 showed a diffuse pattern (18 differentiated, 40 undifferentiated). Our results confirm previous literature data indicating a better efficacy of histology versus morphology in detecting residual bone marrow disease (especially in case of focal differentiated pattern). The recent introduction of a specific monoclonal antibody, called anti-GD2, has improved our capacity to detect minimal residual disease in patients' bone marrow. The inclusion of anti-GD2 immunohistochemistry in our evaluation will possibly increase our overall sensitivity to detect minimal residual disease and may provide information capable to direct the physician's decision into a more rational patient's treatment.