BackgroundImpaired kidney concentration capacity is present in half of the patients with autosomal dominant polycystic kidney disease (ADPKD). The kidney concentrating capacity was further impaired within the animal model of autosomal recessive polycystic kidney disease (ARPKD). To date, only one small study has investigated it in children having ARPKD. Therefore, we aimed to study the kidney concentrating ability in a larger cohort of children with ARPKD.MethodsEighteen children (median age 8.5 years, range 1.3–16.8) were retrospectively investigated. A standardized kidney concentrating capacity test was performed after the application of a nasal drop of desmopressin (urine osmolality > 900 mOsmol/kg). The glomerular filtration rate was estimated using the Schwartz formula (eGFR) and blood pressure (BP) was measured as office BP.ResultsKidney concentrating capacity was decreased (urine osmolality < 900 mOsmol/kg) in 100% of children with ARPKD. The median urine osmolality after desmopressin application was 389 (range 235–601) mOsmol/kg. Sixteen patients (89%) were defined as hypertensive based on their actual BP level or their use of antihypertensive drugs. The maximum amounts of urinary concentration correlated significantly with eGFR (r= 0.72,p< 0.0001) and hypertensive scores (r= 0.50,p< 0.05), but not with kidney size. Twelve patients (67%) were defined as having CKD stages 2–4. The median concentrating capacity was significantly lower in children within this group, when compared to children with CKD stage 1 possessing a normal eGFR (544 mOsmol/kg, range 413–600 mOsmol/kg vs. 327 mOsmol/kg, range 235–417 mOsmol/l,p< 0.001).ConclusionsImpaired kidney concentrating capacity is present in most children with ARPKD and is associated with decreased eGFR and hypertension.Graphical abstractA higher resolution version of the Graphical abstract is available asSupplementary informationSupplementary informationThe online version contains supplementary material available at 10.1007/s00467-022-05834-5.