An association between the rare condition of transient neonatal diabetes mellitus and either uniparental disomy for chromosome 6 or dup(6)(q22q23) raised the assumption that in this location on chromosome 6 there is an imprinted gene. We diagnosed diabetes that developed in a baby girl immediately after birth and resolved after 7 weeks of insulin treatment. Due to some minor dysmorphic features, we investigated her karyotype and identified invdup(6)(q22q23). The duplication spans at least 10 cM including the DNA sites DS270,S314,S1684 and S310. This case further supports the assumption that an imprinted gene exists on chromosome 6q22-23.