Ataxia telangiectasia, Nijmegen breakage syndrome and DiGeorge syndrome are congenital disorders belonging to the category of primary immunodeficiencies. They are characterised by remittent infections as well as predisposition to cancer and autoimmune diseases. An important sign of ataxia telangiectasia and Nijmegen breakage syndrome is an increased sensitivity of cells to ionising radiation, while DiGeorge syndrome is additionally characterised by heart defects and endocrine disorders. What all these diseases have in common are dysmorphic features of different severity, which complement the clinical picture. The signs and symptoms of the diseases may be inconclusive, they appear at various stages of life and their course is unique for every individual. The aim of the study was to present the characteristics of each syndrome while drawing special attention to dysmorphic features occurring in patients. It is important for doctors to be able to diagnose characteristic disorders of the phenotype and immune system and to match them to the right genetic syndrome. Therefore, they should take the patient’s medical history properly, perform thorough physical examination and use multiple diagnostic tools. Despite the fact that these syndromes are rare and incurable disorders, fast and accurate diagnosis gives patients a chance for an improved quality and length of life. The treatment is only symptomatic, but proper prevention can help to avoid the development of a cancer. Therefore, it is of vital importance for the general practitioners, paediatricians and other specialists to know the characteristic signs and symptoms of these syndromes and to cooperate closely with the patients’ parents.