High success rates exceeding 90% are reported with percutaneous nephrolithotomy (PNL) and modifications have further decreased the morbidity while maintaining efficacy. However, complications after or during PNL may occur with an overall complication rate of up to 83%. Although results from several large series on PNL from outstanding centers are reported in the literature, there is still no consensus on how to define complications and stratify them by severity. Hampering comparison of outcome data may generate difficulties in informing the patients about the severity of PNL complications. We therefore may conclude that standardization of complications of a certain procedure is necessary to allow comparison of outcomes between different centers, within a center over time, or between different instruments used and/or operating techniques. In 1992, Clavien et al proposed general principles to classify complications of surgery based on a therapy-oriented, 4-level severity grading, allowing identifying most complications and preventing down rating. The Clavien Classification system differentiates in five degrees of severity upon the intention to treat. Several Urological teams have studied the use of classifications systems to document and grade outcomes and morbidity of interventions in urology. Also the modified Clavien system has been applied in urological surgery. Urologists have been using this classification to grade perioperative complications following laparoscopic radical prostatectomy, laparoscopic live donor nephrectomy, and retroperitoneoscopy. In the field of endourology, it has been recently applied to PCNL procedures as well, allowing comparison among different series between different hospitals and within the same center. Other benefits that the standardization of the complications by using the Clavien System allows is to give better information to the patient and, assisting them on making the correct therapeutical choice. There may also be a benefit for the health insurance bodies to obtain adequate information of the procedure, and the results achieved by a team. Besides all its benefits, the modified Clavien system was proposed as a grading system for perioperative complications in general surgery and there are some limitations in classifying PCNL complications. A graded classification scheme for reporting the complications of PCNL may be useful for monitoring and reporting outcomes. There are some limitations in classifying PCNL complications. Minor modifications, especially concerning auxiliary treatments, are needed. Further studies are awaited for the development of an accepted classification system applicable to all urologic procedures.