Data collection for the national registry for patients with primary immunodeficiency disorders in the Republic of Ireland commenced in 1996. One hundred and fifteen cases of primary immunodeficiency diseases were registered between December 1996 and February 2003. The most frequent primary immunodeficiency disorders were antibody deficiency (n = 53) and complement deficiency (n = 32). In addition, patients with T cell deficiency (n = 11) and chronic granulomatous disease (n = 11) were identified. A small number of patients with Wiskott-Aldrich syndrome, natural killer cell deficiency, DiGeorge syndrome and chronic mucocutaneous candidiasis were also registered. Comparison of our data with that recently reported in the European registry revealed that complement deficiency was more prevalent in the Republic of Ireland compared to other European countries. Results of our registry point to a significant prevalence of primary immunodeficiency disorders in the Republic of Ireland (2.9 cases per 100,000 population). However, it is likely that these figures underestimate the true prevalence of such cases in the country. We hope, with increased awareness of the national registry among primary care physicians, that more patients will be included and we will be able to identify accurately the frequency and the distribution of these disorders.