Adult T-cell leukemia/lymphoma (ATLL) is an aggressive hematologic malignancy linked to HTLV-1 infection, which is refractory to therapy. The precise mechanism of oncogenesis in ATLL is incompletely understood, however, oncogenic viral genes Tax and Hbz are implicated, and recent large genomic and transcriptome studies provide further insight. Despite progress in understanding the disease, survival and outcome with current therapies remain poor. Long-term survivors are reported, primarily among those with indolent disease or activating CC chemokine receptor 4 mutations, however, allogeneic hematopoietic stem cell transplant is the only curative treatment option. The majority of patients succumb to their disease and ongoing and collaborative research efforts are needed. I will review recent updates in HTLV-1-associated ATLL epidemiology, pathogenesis, therapy, and prevention.