A population-based case-control study was conducted to evaluate risk of developing chronic lymphocytic leukemia (CLL) associated with personal and/or family history of autoimmune and related diseases. Data were obtained for all (n = 7764) patients diagnosed with CLL in Sweden and Denmark over a 40-year period and with linkable relatives, 16,658 matched control subjects, and first-degree relatives of patients (n = 17,991) and control subjects (n = 39,388). Odds ratios (ORs) were calculated to quantify risk of CLL in relation to personal/family history of 32 autoimmune and related disorders. The risk of CLL was significantly increased among subjects with a personal history of pernicious anemia (OR = 1.94; 1.18-3.18), mainly in the 0- to 1-year latency period. A significantly decreased risk of CLL was found among individuals with a personal history of chronic rheumatic heart disease (OR = 0.55; 0.33-0.93), particularly persons with a long latency (10+ years) between the 2 conditions. We found no association between personal or familial occurrence of other autoimmune or related disorders and CLL. If our results are confirmed, mechanistic studies examining how pernicious anemia might promote increased occurrence of CLL and how chronic rheumatic heart disease protects against CLL, perhaps related to long-term antibiotics use, may provide insights to the as-yet-unknown etiology of CLL.