Ultrasound shows mild hydronephrosis on left kidney. a stone measuring 5x3 mm at lower end of left ureter. will it come out itself?

It may: It has gone most of he way, but could be stuck where the drainage tube crosses the pelvic brim.

Dr Ali and another doctor agreed

Possible: As size increases, it is less likely to pass on its own. A good rule of thumb is that a 5 mm stone will pass 50% of the time. This decreases to 10% at 9 mm.

Probably: Over 95% of stones less than 5mm in diameter will pass spontaneously over 4 week period. However persistent severe flank pain, even with a tiny stone may indicate need for urologic intervention. 50% of stones > 5mm will not pass sponaneously. Approximately 80% of stones reaching ureterovesical junction pass spontaneously almost regardless of size. Compares to < 50% of stones in proximal ureter.