We report a case of a 7-year-old boy with a voluminous 8.5-cm “cobra-head” calculus in a duplex system ureterocele causing flank pain, hematuria, and infection. Combined cysto-ureteroscopy and percutaneous cystolithotomy enables dependent ureterocele incision along its inferolateral border and efficient stone clearance in a single minimally invasive procedure. Protracted and repeated urethral instrumentation is avoided.