Bloom syndrome is a rare autosomal recessive syndrome characterized by proportional dwarfism, characteristic facial findings, photosensitivity, telangiectasia, well-circumscribed dermal hypo-or hyperpigmented lesions, immunodeficiency, and infertility. Ten-and 3-year-old sibling patients were thought to have Bloom syndrome due to failure to thrive, cafe-au-lait spots and giant nevi on the legs. The older sibling was operated for Wilms' tumor at 4 years of age. The diagnosis was confirmed with increased sister chromatid exchanges in peripheral blood cells in both cases. In patients with Bloom syndrome, prevention of recurrent respiratory and gastrointestinal infections and close monitoring of the patients regarding immunodeficiency and endocrinologic diseases are important issues. In Bloom syndrome, the mutation in the 15q26.1 region of the BLM gene, leading to protein loss and increased frequency of sister chromatid exchanges, promotes malignancy formation. Minimization of sun exposure is important in terms of malignancy development, which is the main cause of deaths in the 2nd and 3rd decades. In this report, we aimed to present information about the clinical findings, prognosis and immunological features of Bloom syndrome.