Hi, Thanks for writing in. The collecting system of the kidney is made of renal calyces and pelvis. This collects the urine formed in kidney and transports it through the ureter (tubes connecting kidneys and urinary bladder) to the urinary bladder. The pelvicalyceal system is the mouth of the kidney where it connects with the upper end of the ureter. I guess that you have got ultrasound scan done and it shows mild fullness of the pelvicalyceal system in the left kidney, that is a term applied to increase in diameter of the collecting system in your left kidney. It is not a critical situation and please do not worry if you do not have any urinary symptoms. Since it is mentioned as mild fullness and no kidney stones have been found, therefore (i) It can be that your bladder was completely full at the of ultrasound scan (ii) Your kidney pelvicalyceal system is appearing full by itself (extrarenal pelvis) and is an extension of normal appearance. (iii) Rarely an infection of urinary system and kidneys (recent or old) can cause such a finding but this is likely only if you have symptoms like pain in the region of kidney and problems like burning urination or discoloration of urine or any kidney infections in the past. (iv) Stones in kidney or ureter can also cause fullness of pelvicalyceal system and since you do not have any stone therefore this does not apply to you. It is important to know if your scan was repeated after passing urine ans still there was persistent mild fullness of the pelvicalyceal system on left side. This can also be confirmed by doing an IVP which is injecting a contrast and taking 5 to 6 X rays to study the functioning of the kidneys in a better way. Please consult the urologist.