AbstractThe annual incidence of neuroblastoma in Japan, a common malignancy of young children which has a very poor prognosis in progressive cases, was previouly estimated to be 8.2 cases/million children under 15 years of age. Based on the Japanese National Census of the Population for 1982, the annual number of cases of this tumor is predicted to be 220. (Sawada et al:Med Pediatr Oncol12:101‐103, 1984). Before the mass screening program was started, one‐fourth of all neuroblastoma cases were detected before the age of one by clinical symptoms and other findings.Since 1974, a neuroblastoma mass screening program for 6‐month‐old infants by means of a qualitative Vanilmandelic Acid (VMA) test has been in effect in Kyoto, Japan, for the prognostic improvement of neuroblastoma patients (Sawada et al:Am J Dis Child136:710‐712, 1982). A Neuroblastoma Mass Screening Study Group (NBMSSG) was organized in 1981 (Sawada et al:Lancetii:271‐272, 1984), and the mass screening program has grown to encompass eight selected areas. This group discovered 15 cases of neuroblastoma among 247,500 6‐month‐old infants, 1 of every 16,500, until the end of 1983, and 23 cases among 434,970, 1 of every 18,900, until the end of 1984. All cases were asymptomatic. As the incidence of infantile neuroblastoma detected by this program is projected to be 52.9‐60.6 cases/million 6‐month‐old infants, it could be predicted that 80‐91 neuroblastoma cases will be discovered annually in Japan by mass screening. The cure rate of 25 cases discovered by the mass screening and followed up over 20 months was 92% (Sawada:Lanceti:377, 1986).In Japan, it should be possible to detect 135‐146 cases‐[symptomatic 55 = 220 × 1/4] + [80‐91 cases detected by mass screening]‐(61.4‐66.4% of the total neuroblastoma cases) in infants under 1 year of age annually, and the cure rate of all neuroblastoma cases in Japa