Dehydration. Having an excess of stone-forming substances in the urine, such as high concentrations of calcium oxalate or phosphate, uric acid or cystine. Certain diseases like gout or hyperparathyroidism. Having had surgeries that take out or bypass part of the small intestine (this is why I get them). Men get them more frequently than women, particularly middle-aged men.
Kidney Stones (Renal Stone) Causes, Symptoms, Treatment, and Prevention on MedicineNet.com