Primary immunodeficiencies in children are rare, but an early diagnosis can improve long-term quality of life and prevent rapid deterioration of the immune system. More than 70 immunodeficiency diseases have been identified and are classified according to the areas of the immune system that are compromised. When a suspicious history or an uninterrupted pattern of infections leads the practitioner to suspect immunodeficiency, it is essential that proper immunologic testing be initiated as soon as possible. Once a diagnosis is established, the practitioner and a team of experts all are involved in the multidisciplinary treatment, counseling, and longitudinal care of children with primary immunodeficiency.