Abstract Mutations in PTPN11, which encodes the protein tyrosine phosphatase SHP2, contribute to ∼35% of cases of juvenile myelomonocytic leukemia (JMML). A common clinical picture in children with JMML is that it presents as a constitutive hyperinflammatory syndrome, partially reminiscent of chronic myelomonocytic leukemia in adults. Thus, a component of JMML is associated with a hyperinflammatory state and abundant innate immune cells such as neutrophils and monocytes. Recently, we showed that the evolutionarily conserved mouse lncRNA Morrbid is specifically expressed in myeloid cells and uniquely represses the expression of the proapoptotic gene Bim to regulate the lifespan of myeloid cells. However, its role in JMML has not been investigated. In this study, we characterized the role of Morrbid and its target Bim, which are significantly dysregulated in Shp2E76K/+-bearing myeloid cells, in driving JMML. Loss of Morrbid in a mouse model of JMML driven by the Shp2E76K/+ mutation resulted in a significant correction of myeloid and erythroid cell abnormalities associated with JMML, including overall survival. Consistently, patients with JMML who had PTPN11, KRAS, and NRAS mutations and high expression of MORRBID manifested poor overall survival. Our results suggest that Morrbid contributes to JMML pathogenesis.