We describe a case of a partial unilateral duplex system and ureterocele containing a 4 cm stone in a 66-year-old woman who presented with renal colic. Cystoscopic stone removal and deroofing of the ureterocele were performed and a ureteral stent was placed for a total of 6 weeks. Our case is unique as it highlighted the diagnostic pitfalls of ureteroceles, especially when obscured by a large calculus. We also described the use of a Holmium laser to simultaneously incise the ureterocele and fragment the calculus.