Kidney stone 0.9cm may or may not be serious. If the kidney stone grows at the neck of the kidney calyx, it may cause fluid accumulation in the kidney calyx, which needs to be treated at this time. If the kidney stone of 0.9cm grows inside the renal pelvis, it may be more serious, because it will cause obstruction of the urinary channel, then it needs to be treated surgically. If a 0.9 cm kidney stone grows in the lower renal calyx, it may not be serious because it will not block the urinary passage of the kidney, so no special treatment is needed.