IgA deficiency (D-IgA) in the paediatric population is often an occasional finding during tests performed for other reasons in children in whom an immunodeficiency disorder is not suspected. D-IgA is the most common primary immunodeficiency with a variable prevalence according to ethnicity, estimated on 1 case/600 in the Caucasian population. IgA should be dosed twice in a child > 4 years of age to confirm the deficiency, which is defined by the presence of serum IgA < 0.07 g/l. The other classes of immunoglobulins should always be dosed. Most patients with D-IgA will not require any treatment or follow-up (85% are asymptomatic), apart from screening for coeliac disease, which is 10 to 20 times more frequent in patients with D-IgA. In the case of a child with D-IgA with recurrent infections (mainly affecting the respiratory and, less commonly, the gastrointestinal tract), signs and symptoms of alarm must always be sought and valued for other types of primary immunodeficiency (especially the common variable immunodeficiency), which, although rarely, can be associated with D-IgA. Patients with D-IgA, in particular adolescents and adults, have a higher risk than the general population of developing autoimmune diseases. The family should be informed of this possible occurrence, but specific laboratory evaluations are not necessary. Four clinical cases are presented: an occasional finding of D-IgA in a healthy child, the association with coeliac disease, the association with juvenile idiopathic arthritis, and IgA deficiency in a patient with an immunodeficiency disorder (ataxia-telangectasia).