Spontaneous remission of chronic lymphocytic leukemia (CLL) is an unusual and poorly characterized event. We performed a search for spontaneous remission in patients with CLL. Cases must have had a pathological diagnosis of CLL with disease duration > 6 months. Spontaneous remission was defined as absence of lymphadenopathy or splenomegaly with lymphocyte counts < 5 × 10(9)/L for > 9 months without therapy. We identified 20 cases and included one additional case from our institution. Fourteen cases (67%) showed remission into monoclonal B lymphocytosis (MBL) and seven (33%) into a normal phenotype. There was no difference in age distribution, lymphocyte count or stage between groups. There was a significant difference in the median duration of CLL prior to remission, 13 years in the MBL versus 3 years in the normal phenotype group (p = 0.03). This difference in the duration of CLL prior to remission could be due to a possible distinct pathophysiology for these events.