Chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) is a generally indolent neoplasm of mature B lymphocytes that primarily affects older adults but rarely occurs in adolescents and young adults. We report a case of CLL/SLL in an 18-year-old patient treated with venetoclax, an orally bioavailable BCL-2 inhibitor, in combination with obinutuzumab, a humanized anti-CD20 monoclonal antibody. The patient experienced rapid clinical response and after one year of therapy had no evidence of residual disease by radiographical imaging and bone marrow evaluation. This finite, targeted therapeutic approach is an attractive option for future adolescent patients with CLL/SLL.