By renal ultrasound examination, urological anomalies may be demonstrated in 1-2% of fetuses and in about 0.5% of newborns. Boys have about twice the frequency of girls. Surgical treatment is indicated in about one fourth of these urological anomalies. If all pregnant women in Denmark were to have fetal ultrasound examination of the kidneys and the urinary tract, about 70 children would be born each year with a prenatally diagnosed urological anomaly for which surgical procedure is or will be indicated. This paper provides Danish guidelines for prenatal diagnosis, follow-up and intervention in cases of urological anomalies and guidelines for post-natal diagnosis, follow-up and treatment of these anomalies, especially hydronephrosis.