Common Variable Immunodeficiency belongs to the group of rare diseases encompassing antibody deficiency syndromes of highly variable clinical presentation and outcome. The multicenter prospective study on a cohort of 224 patients with Common Variable Immunodeficiency provides an updated view of the spectrum of illnesses which occurred at the clinical onset and over a long period of follow-up (mean time: 11 years) and information on the effects of long-term immunoglobulin treatment. The mean age at the time of diagnosis was 26.6 years. Seventy-five patients were younger than 14 years of age. The mean age at the onset of symptoms was 16.9 years. This implicates with a mean diagnostic delay of 8.9 years. Respiratory tract infections were the most prominent clinical problem observed at diagnosis and during the follow-up. Intravenous immunoglobulin administration induced a significant reduction in the incidence of acute infections, mainly acute pneumonia and acute otitis. However, a progressive increase in the prevalence of patients with chronic diseases, mainly sinusitis and lung disease, was observed in all age groups, including the pediatric population. The morbidity of Common Variable Immunodeficiency due to all associated clinical conditions increased over time despite an adequate replacement with intravenous immunoglobulins. Our data stressed the need to develop international guidelines for the prevention and therapy of chronic lung disease, chronic sinusitis, chronic diarrhoea, and chronic granulomatosis in patients with humoral immunodeficiencies.