The proband in this study had multiple congenital malformations and a constitutional 46,XY,-13, + der(13),t(13;15)(q34;q23)mat chromosome complement. A bone marrow aspirate revealed neuroblastoma, and cytogenetic studies on tumor cells revealed, in addition to the partial trisomy #15 and probable partial monosomy #13, hypotetraploidy with a mean chromosome number of 82-84, including 3 or 4 copies of each autosome, 2 X chromosomes, no Y chromosome, and a marker. Translocations involving chromosomes #1, #2, #3, #7, and #14 were present, along with multiple double minutes. The possibility that the inherited partial trisomy #15 (and/or partial chromosome #13 monosomy) predisposed to neuroblastoma and additional chromosome changes in this tumor is discussed.