To assess reliability of Guy's, Seoul National University renal stone (S-RESC) and S.T.O.N.E. scores in percutaneous nephrolithotomy (PCNL) and assess utility in discriminating outcomes [Stone free rate (SFR), complications, need for multiple PCNL sessions and auxiliary procedures] valid across parameters of experience of surgeon, independence from surgical approach, and variations in institution-specific instrumentation.