Autosomal dominant polycystic kidney disease(ADPKD) is rarely observed in the neonatal period. We report 2 cases of ADPKD who showed bilateral enlarged, hyperechoic kidneys and severe hypertension. It is difficult to differentiate ADPKD from autosomal recessive polycystic kidney disease (ARPKD) based on the initial clinical presentations in this period. In both cases, bilateral enlarged kidneys and severe hypertension were detected without oligohydramnion and respiratory distress. The mother of case 1 has polycystic kidneys. The father of case 2 was diagnosed as ADPKD. Case 2 had heart failure due to hypertension. Angiotensin converting enzyme inhibitor (ACE-I) was administered to both patients and resulted in good control of blood pressure. ADPKD in the neonatal and very early infantile period has diverse clinical courses. In general, although severe cases are rare, some cases have renal failure and/or hypertension as we reported. We emphasize that both the prompt diagnosis of ADPKD and the start of medication are of great importance in the neonatal and very early infantile period. We recommend that neonates and infants with a family history of ADPKD undergo screening including physical examinations, blood pressure measurements and urinalysis.