Lenalidomide is effective against relapsed chronic lymphocytic leukemia (CLL). We report the first case of long-term molecular remission with continuous lenalidomide treatment in a young patient with CLL relapsed to multiple treatments. Minimal residual disease was assessed by nested polymerase chain reaction on bone marrow samples with patient-specific primers. A 20-yr-old patient with standard-risk CLL was treated with lenalidomide after multiple relapses and achieved a 4 yr long complete molecular response with minimal toxicities. Published biologic data support that lenalidomide induces an immune-mediated control of CLL, and our case suggests that long-term treatment with lenalidomide is effective at a molecular level in patients with relapsed CLL.