The article presents a rare case of type II mucopolysaccharidosis (MPs) in children. From the age of one and a half, the child was observed by an ENT doctor for 2–3 degree adenoids. At the age of 2, an adenotomy was performed. In the future, a relapse of adenoid hyperplasia. 1 year of age according to the ultrasound revealed hepatosplenomegaly. At the age of three years, type 2 mucopolysaccharidosis was suspected, which was confirmed on the basis of increased levels of heparan sulfate and dermatansulfate in the urine, molecular genetic diagnostics (mutation in exon 3 of IDS Lis135Glu in the hemizygous state. Appointed replacement therapy: Elaprase. Clinical polymorphism, different severity of symptoms combined with rare occurrence cause certain difficulties in early identification of MPs-II. Timely diagnosis is extremely important for referral of such children to specialists of an interdisciplinary center who have experience in specific treatment that is most effective in the early stage of the disease.