Hepatocyte nuclear factor 1β (HNF1β)-associated disease is a rare autosomal dominant disease caused by various mutations in the HNF1β gene coding the hepatocyte nuclear factor 1β. HNF1β is a transcription factor that is critical for the development of kidney urogenital tract, pancreas, liver, brain, and parathyroid gland. Renal phenotype or HNF1β- nephropathy appeared to be extremely heterogenic: multicystic renal dysplasia, renal hypoplasia, unilateral renal agenesis, horseshoe kidney, atypical familial juvenile hyperuricemic nephropathy, urinary tract malformations and tubular dysfunction. Extrarenal phenotype of HNF1β-associated disease could be maturity-onset diabetes of the young (MODY), pancreatic atrophy and exocrine pancreatic dysfunction, elevated liver enzymes, neonatal cholestasis, congenital abnormalities of the genital tract, hyperparathyroidism, neurological symptoms. The multisystem phenotype makes clinical verification of the diagnosis extremely difficult. In this article, we present a clinical observation of a child with HNF1β – associated disease. The first clinical presentation of HNF1β-associated disease was ultrasound changes in the kidneys (hyperechogenic kidneys?), which were detected by prenatal ultrasonography in pregnancy. Renal ultrasound revealed polycystic kidney disease in the first days of life and bilateral medullary nephrocalcinosis by the age of three. The clinical examination showed a reduced renal function and developed Fanconi syndrome (glycosuria, low molecular proteinuria, hypophosphatemia, aminoaciduria, hyperuricosuria) in the first year of life. Also the child had a non-constant asymptomatic elevation of liver enzymes, hyperparathyroidism, osteoporosis. The diagnosis was confirmed by the results of next generation sequencing which revealed novel heterozygous mutation in exon 4 of the HNF1b gene (chr17: 36091813C>T), p.Cys273Tyr (c.818G>A). The identified mutation was validated by Sanger sequencing. Validation by Sanger sequencing did not reveal a chr17: 36091813C>T mutation in parents, which suggested the appearance of a mutation in the child de novo.