RESUMEN
BACKGROUND: Congenital malformations of the kidneys and urinary tract may have changed over time. MATERIAL AND METHODS: Data for diagnosis, treatment and results were retrospectively recorded in children born in one of three Norwegian counties 1987-2006; their age at time of recording was from 1 to 21 years. RESULTS: 389 of 142 986 (2.7 per 1000) live born children had malformations of the kidneys and/or urinary tract. The prevalence was higher for children born in the period 1997-2006 (241/70 217; 3.4 per 1000) than in 1987-1996 (148/72 769; 2.0 per 1000), p< 0.0011. The percentage of children with anomalies diagnosed prenatally increased significantly from the first born 10-year cohort (35/148; 24 %) to the last (125/241; 52 %), p < 0.0011. Urosepsis occurred in 8 (1.1 per 1000) patients in the first 10-year cohort and in 9 (1.3 per 1000) patients in the last cohort (p = 0.75). 137 (35 %) patients had undergone surgery, of whom 68 (0.9 per 1000) were born 1987-96 and 69 (1 per 1000) were born 1997-2006. Chronic renal failure developed in 6 patients (0.1 per 1000) in each 10-year cohort; 4 (0.05 per 1000) and 11 (0.16 per 1000) patients died in the two cohorts (p = 0.07) respectively. INTERPRETATION: More frequent use of prenatal ultrasound screening has caused a 69 % increase in the prevalence of malformations in kidneys and the urinary tract. The number of patients treated by surgery, deaths and the prevalence of urosepsis and chronic renal failure has remained unchanged. This may indicate increased detection of less severe malformations.