Genetic alterations cause predisposition to malignancy by increased cancer risk related to constitutional mutations in growth-regulating or DNA repair genes. Some pediatric malignancies are associated with dysmorphic features in several body areas. Through physical examination, we recognise characteristic signs of genetic dysmorphic disorders, such as somatic overgrowth, undergrowth, macrocephaly, microcephaly and dysmorphic changes of the face, eyes, mouth and lips, heart, gastrointestinal tract, urinary tract, genitalia and skeleton. Recognition of a cancer-associated dysmorphic syndrome allows intensive cancer screening and genetic counseling. Therefore, it is recommended that every child with cancer should be examined by a clinical geneticist. Molecular diagnostics of germinal mutations may very effectively detect families at high risk of malignancy and help provide primary prevention. This work presents clinical syndromes with genetic background and cancer screening recommendations for 18 syndromes with increased cancer risk.