Aim: To explore the possibility of reducing the diagnostic burden in children with prenatally detected unilateral ureteropelvic junction obstruction. Methods: Children with unilateral ureteropelvic junction obstruction (2012-2020) were identified from a prenatal hydronephrosis registry. The frequency of adverse events, predictors for event-free follow-up beyond 1 year of age, and examination burden in children with conservatively managed unilateral ureteropelvic junction obstruction were assessed. Adverse events included febrile urinary tract infections, > 10% decline in differential renal function, or both, leading to surgery. Follow-up ended at clinical conclusion or surgical decision. Results: Forty-seven children were included, with a follow-up of median 22.5 (2-115, min-max) months. Overall, 43% (20/47) had no adverse events. Adverse events occurred within 2 years in 85% (23/27). Predictors of event-free follow-up beyond 1 year were a postnatal anteroposterior diameter < 15 mm at 12 months (p < 0.001) or a stable anteroposterior diameter during the first year (p = 0.04). Patients without adverse events underwent a median of eight (3-26, min-max) diagnostic imaging examinations. Conclusions: In children with antenatally detected ureteropelvic junction obstruction, 43% had no adverse events, but a substantial examination burden. Predictors of a non-eventful trace, useful in guidelines, were a postnatal anteroposterior diameter < 15 mm or stable at 12 months.