Japan has a nationwide mass-screening program for neuroblastoma in 6-month-old infants. Neuroblastoma can regress spontaneously, and some institutions observe selected cases. We evaluated the management of screened neuroblastoma at our hospital since 1997 when an observation program was introduced. Criteria for the observation program were stage-I, stage-II, or stage-IVs tumors, urinary vanillylmandelic acid (VMA) and homovanillic acid (HVA) levels <40 microg/mg creatinine, tumor <5 cm in diameter, no invasion to the intraspinal canal or great vessels, and parental consent to participate. Patients who did not meet observation criteria underwent surgery or mild chemotherapy according to the location of the tumor. If patients met observation criteria after chemotherapy, surgical intervention was no longer performed. Thirty-six patients attended our hospital for screened neuroblastoma from 1997 to 2002. Thirty-three patients who were managed at our hospital participated in this study. Ten subjects met observation criteria. Tumors regressed in 7 patients (mean follow-up period 36.3 months) with corresponding decreases in VMA and HVA levels (group A). Three underwent surgery (group B) because of increasing VMA and HVA levels, increase in tumor size, or guardian's request. Twenty-three subjects did not meet observation criteria. Four patients underwent primary surgery (group C), and 19 patients had chemotherapy initially. Fourteen patients met observation criteria after chemotherapy and two are still having chemotherapy (group D). Three patients required surgery due to insufficient regression of their tumors (group E). Fourteen subjects in group D had marked decreases in VMA and HVA levels and tumor size (mean follow-up period 29.1 months), and tumors were not detected using imaging techniques in 8 patients. Histological examination of all resected specimens during the study period showed favorable histology and no N-myc amplification. There was no evidence of unfavorable prognosis in any of the 33 subjects, although 1 patient who underwent primary surgery had a vanishing kidney 1 year later and 1 patient had multiple bony metastases after complete resection of tumor, which was treated by chemotherapy. Until the real significance of mass screening for neuroblastoma as a public health measure is confirmed, observation with careful follow-up should be adopted more extensively because it has a favorable outcome in many cases, and is associated with minimal therapeutic complications.