Aim: to develop a simple and reliable system for predicting the results of percutaneous nephrolithotripsy (PNL). Materials and methods. The analysis of 138 patients, who underwent PNL (standard method) over the period of 2011-2015, was performed. Low-dose non-contrast multispiral computed tomography (MSCT) was performed in all patients during the post-operative stage, 24 hours a?er PNL.?e presence ofresidual concrements(≤ 4 mm) ortheirtotal absence in kidneyswasregarded as a criterion for effective concrement elimination. Results. According to the data obtained from MSCT, the patients were divided into two groups. The first group (88 patients) included those who did not have residual concrement fragments after PNL or who had clinically insignificant residual concrement fragments. The second group included 55 patientswith residual concrement fragments. Among the parameters used in the study, the most informative were:

• The presence of a stone in renal calyx in a ≤ 450 position («acute angle» – A)
• The presence of a stone (≥ 10 mm) in renal calyx with a narrow (≤ 8 mm) isthmus («complicated calyx» – C)
• The size of a stone ≥ 23,5 mm («size» – S)

These three parameters were designated as ACS. ?e presence or absence of one of these parameters was counted as 1 or 0,respectively. For example, if the overallACS score is 0, then the probability of achieving the “Stone free” stage after PNL is 91%. In contrast, if ACS score is 3 (when all three parameterswere present), this probability is only 10%. Unfortunately, intermediate ACS scores (1 and 2) did not have any prognostic significance. Conclusion.The use of theACS system in the routine clinical practice is regarded as a simple and reliable instrument which allows to dresict the results of percutaneous nephrolithotripsy. Authors declarelack of the possibleconflicts of interests

Authors declare lack of the possible conflicts of interests.