OBJECTIVE To determine the association between a history of asthma and a diagnosis of selective IgA deficiency (sIgAD)/common variable immunodeficiency (CVID). METHODS This population-based case-control study included residents of Olmsted County, Minnesota, who met the Pan-American Group for Immunodeficiency/European Society for Immunodeficiencies diagnostic criteria for sIgAD/CVID between January 1, 1964, through December 31, 2008. Each case had 4 age- and sex-matched controls (2 from the community and 2 from a list of individuals who had undergone an immune work-up). We ascertained asthma status by applying predetermined criteria for asthma. RESULTS We identified 39 cases: 26 (66.7%) had sIgAD and 13 (33.3%) had CVID. Of the 39 cases, 51.3% were men (n=20) and 97.1% were white (33 of 34 patients). The mean age at the index date (the time when criteria were met) of sIgAD/CVID was 34.2 years. Of the 39 cases, 9 (23.1%) had a history of asthma before the index date of sIgAD/CVID; of the 156 controls, 16 (10.3%) had a history of asthma before the index date (odds ratio, 2.77; 95% CI, 1.09-7.06; P=.03). A history of asthma (before or after the index date of sIgAD/CVID) was more prevalent in sIgAD/CVID cases (30.8%; n=12) than in matched controls (11.5%; n=18) (odds ratio, 3.57; 95% CI, 1.50-8.51; P=.01). CONCLUSIONS Asthmatic patients are more likely to have a diagnosis of sIgAD/CVID than nonasthmatic individuals. This association may potentially account for the increased risks of bacterial infections in some individuals with asthma.