The ultrasonographic (US) findings of 25 infant cases detected by the Japanese mass screening program for neuroblastoma (NB) were reviewed. The following results were obtained: An identification of the primary site was possible in 96% of the cases with abdominal US. An estimation of the tumor weight was possible based on the mass volume, which was calculated from US measurements. With the combination of the estimated mass volume, local involvement, and distant metastasis, the US grading of NB was possible and closely corresponded to the surgical staging (84%). The NB cases of adrenal origin at U1a, with a mass volume of less than 16 mL, were all found to be stage I and presented the possibility for spontaneous regression.