Objective:To investigate the typing and clinical value of posterior group renal calyces.Methods:From April 2020 to June 2021, 640 patients (320 men and 320 women) who underwent CTU examination in our hospital with kidneys on both sides and normal or only mild hydronephrosis in the collecting system were analyzed. A total of 1 280 renal CTU three-dimensional reconstructed images were counted.The patients aged 52.4±11.9 years. The patients' CTU images were reconstructed in three dimensions using the spine as a marker to rotate the collecting system images in stereoscopic space to simulate a prone position. A two-person review was taken to observe the imaging morphology of the renal calyces in the prone position, and the 640 renal calyces in the posterior group of the left and right sides were counted for staging. Based on the morphology of the renal calyces and the influence on the establishment of surgical access, the posterior group of renal calyces was divided into 3 major types. Pot-belly type: the renal pelvis is shaped like a pot-belly, and the renal pelvis is directly connected to the cup-shaped minor calyces without a distinct major renal calyces. Classically branched: 2 or more major renal calyces are branched and converge to form the renal pelvis. Elongated branched: the major calyces are branched, with at least one major calyces having an axis length ≥0.9cm and a neck width ≤0.3cm.The classic branching type is divided into three types, a, b, and c, including seven subtypes, based on the relationship of the posterior group of the minor calyces to the major calyces. Type a is derived from group 1 major calyces only, type b is derived from group 2 major calyces at the same time, and type c is derived from the upper, middle and lower groups of major calyces at the same time. Type a contains 3 subtypes.Type a1 is derived from the upper group of major calyces only, type a2 is derived from the middle group of major calyces only, and type a3 is derived from the lower group of major calyces only. Type b is also divided into 3 subtypes. Type b1 is derived from the upper and middle groups of major calyces at the same time, type b2 is derived from the middle and lower groups of major calyces at the same time, and type b3 for the upper and lower renal major calyces. Type c had no corresponding subtype.Results:Statistical findings revealed that all kidneys had posterior group calyces. The morphological typing of the posterior group of calyces was 8.83% (113/1 280) for the pot-bellied type, which had the highest occurrence of 2 minor calyces (5.63%, 72/1 280). 71.25% (912/1 280) had the classically branched type, which had the highest occurrence of 3 minor calyces (31.17%, 399/1 280). 19.92% (255/1 280) had the elongated branched type, with the highest percentage of 3 occurring in the calyces (9.92%, 127/1 280). The anatomical typing of the classical branching type occurred in 20.50% (187/912) for type a, 66.45% (606/912) for type b, and 13.05% (119 /912) for type c. The percentage of occurrence of type a1/a2/a3 was 4.06% (37/ 912), 6.14% (56/ 912), and 10.31% (94/912). b1/b2/b3 types occurred in 2.03% (21/912), 7.46% (68/912), and 56.69% (517/912), respectively.Conclusions:The posterior group of calyces is structurally complex and extremely variable. In this study, the posterior group calyces were found to be present in all patients, and the posterior group calyces were morphologically divided into 3 types, with the highest percentage of occurrence of the classical branching type and the highest percentage of 3 posterior group minor calyces. The classical branching anatomical typing was highest in type b with the highest percentage of type b3, which combined with stone distribution, made it easy to choose the puncture location. The typing of the posterior group of calyces can provide an anatomical basis for PCNL puncture from the posterior group.