Andrioli V, et al. - Experts determined which group of children could be at risk for failure on active surveillance using the data derived by reviewing the patients detected antenatally with ureteroceles. They presumed that single system ureteroceles (SSU) and male patients with duplex system ureteroceles (DSU) would be ideal for observation. For active surveillance (AS), the SSU patients were ideal. However, in DSU, 30% of patients demonstrated successful surveillance who were primarily females without contralateral hydroureter and ipsilateral hydronephrosis ± hydroureter. In the DSU cohort, males were seen to be at higher risk for surgical intervention, a contradiction to the presumption.