Death in Ataxia telangiectasia (A-T) is usually due to cancer or chronic lung failure around 20 years of age. Despite low lymphocyte counts (CD3, CD4, CD8 and CD19), IgA and IgG subclass deficiency opportunistic and acute severe respiratory infections are rare. The prevailing wisdom is that an immunoglobulin replacement therapy is not necessary in most of the patients. However no placebo controlled trials have been performed so far. The aim of this trial was to investigate the prevalence of mild and severe respiratory infections and / or chronic cough in classical A-T patients compared to healthy controls.