Infants with neuroblastoma are known to have a better prognosis than older children. In Japan in 1985, mass screening for neuroblastoma in infants aged 6 months was introduced. With this policy, there has been an increase in the number of patients seen with neuroblastoma between 6 and 11 months of age. In a previous report the authors described the management and prognosis of infants with disease detected by mass screening, but there is still little information regarding the strategies of management for infants with neuroblastoma aged less than 6 months. The authors analyzed the data regarding 27 patients aged less than 6 months registered in their region (population 15 million) from 1985 to 1992, and compared it with that of the previous 8-year period. In the younger age group, there was a significantly higher rate of advanced disease stages (III and IV). In spite of the variation in treatment related to the choice of individual institutions, infants with stages I, II, and III disease had a good outcome, suggesting that aggressive chemotherapy is not necessary unless poor prognostic factors are present. One patient with stage IV disease died of disseminated disease and one with stage IVs and 22 copies of N-myc oncogene also died of tumor relapse in spite of aggressive chemotherapy. It is therefore concluded that the prognosis in infants with stage IV and IVs neuroblastoma under the age of 6 months is not as good as had previously been believed, and that such patients, therefore, require special consideration.