Hi doormouse, I too get them and some reasons are the same as pattytx, two resections and is related to crohns ( isnt everything?) and also hereditary. I have had 3 9mm and one 7mm. I didnt know they were that big, but had lithotripsy and that was the worse pain, (other than a total bowel obstruction) known to man. I got flown to Winnipeg and had it done 3 different times. They say, calcium, and some combos with calcium in water and green tea is a bad mix. I have a RO tap now or drink RO bottled water on the run. The most important thing is to drink alot of water. I have used a natural supplement, but I stopped, it is called Chanca piedra. Dont know if it is effective. No one is alone with this disease, we are here to help because outsiders dont know our pain, litterally! Take care, hang in there, drink lots of water!