Background:Common variable immunodeficiency (CVID) is one of the most common symptomatic primary immunodeficiency syndromes.The purpose of this article was to broaden our knowledge about CVID for better diagnosis and treatment.Methods:Clinical and immunological features of 40 Chinese patients with CVID were analyzed retrospectively.Results:The median age at onset was 11-year-old (range 4-51 years).The median age at diagnosis was 14.5-year-old (range 5-66 years).The average time of delay in diagnosis was 5.3 years (range 1-41 years).The most common main complaint was fever due to infections (35 cases,87.5％).Pneumonia (28 cases,70％) was the most common type of infections.Bronchiectasis was present in 6 patients (15％).Autoimmune disease was detected in 6 cases of CVID,and malignancy in 2 cases.The median total serum levels of IgG,IgA,and IgM at diagnosis were 1.07 g/L,0.07 g/L,and 0.28 g/L,respectively.The percentages ofCD3/CD19+ B-cells were 1％-3.14％.Conclusions:Infection is the most frequent presentation of CVID.Patients with unexplainable infections should receive further examination including serum immunoglobulin (Ig) and lymphocyte subset analysis.Regular and sufficient substitution with Ig is recommended.