Epidemiology

CLL is a disease of older adults and is rarely encountered in individuals under the age of 40. Thereafter the disease incidence increases with age.

In the United States during 2009, about 16,000 new cases are expected to be diagnosed, and 4,400 patients are expected to die from CLL.Because of the prolonged survival, which was typically about ten years in past decades, but which can extend to a normal life expectancy,the prevalence (number of people living with the disease) is much higher than the incidence (new diagnoses).

Subclinical "disease" can be identified in 3.5% of normal adults, and in up to 8% of individuals over the age of 70^{[citation needed]}. That is, small clones of B cells with the characteristic CLL phenotype can be identified in many healthy elderly persons. The clinical significance of these cells is unknown.

Of all cancers involving the same class of blood cell, 7% of cases are CLL/SLL.

Complications: hypogammaglobulinemia leading to recurrent infection, warm auto immune haemolytic anaemia in 10-15% of patients, transformation to high grade lymphoma, Richter's transformation.

Rates of CLL are somewhat elevated in people who have been exposed to certain chemicals. Under U.S. Department of Veterans' Affairs regulations, Vietnam veterans who served in-country or in the inland waterways of Vietnam and who later develop CLL are presumed to have contracted it from exposure to Agent Orange and may be entitled to compensation.