Common variable immunodeficiency is the most common primary immunodeficiency that needs medical attention. Symptoms may occur at any time, with two major peaks of onset at 5-10 and 20-30 years. We present the different clinical phenotypes of common variable immunodeficiency, review recent genetic findings and point to current treatment strategies.Five genes, ICOS, CD19, TNFRSF13B, TNFRSF13C and MSH5, have been found to be mutated in patients with common variable immunodeficiency. Additional possible genetic loci for autosomal dominant forms were detected on chromosomes 4q and 16q. These findings illustrate the heterogeneous molecular basis of common variable immunodeficiency and indicate the value of genetic linkage studies, thereby improving the genetic diagnosis.In young patients with unusually frequent bacterial infections, common variable immunodeficiency should always be considered as a differential diagnosis. The compulsory individual work-up should comprise a family history in order to document siblings and additional family members suffering from common variable immunodeficiency and/or selective IgA deficiency. Since the recently found gene defects affect a minority of patients with common variable immunodeficiency only, future genetic research is required to identify further susceptibility genes involved in the pathogenesis of this condition.