PROJECT SUMMARY Kidney stones can cause severe pain and are associated with kidney injury, infections, and reduced quality of life. The prevalence of kidney stone disease has risen across all demographic groups, especially among women, children, and minorities. All kidney stone patients are at risk for future symptomatic events. Therefore, determining the appropriate preventative strategies to prevent future symptomatic events will improve health and reduce the care-related costs for urinary stone disease. Diet and pharmacologic interventions for preventing future kidney stone episodes are effective, and these interventions are made over a lifetime due to kidney stone disease as a chronic condition. The interventions can be burdensome, have side effects, and have associated costs. Clinical guideline panels disagree on whether clinicians should perform selective therapy: performing 24-hour urine testing to guide choosing interventions to correct abnormal urinary parameters. The alternative strategy is empiric therapy: applying interventions without 24-hour urine testing. No trials have compared selective versus empiric pharmacologic intervention strategies to reduce kidney stone recurrence risk. In contrast, diet studies to date comparing these two strategies have had methodologic flaws limiting their interpretation. Our overall goal is to compare the effectiveness and safety of selective and empiric strategies for kidney stone prevention. The primary outcomes will be mean calculated supersaturations of calcium oxalate and calcium phosphate. Aim 1 will perform a randomized clinical trial of selective versus empiric diet and pharmacologic on therapy patients with presumed idiopathic calcium stones The empiric group will have pre-assigned diet recommendations and daily thiazide with potassium citrate, whereas the selective group will be prescribed an individualized diet and medication regimen as guided by 24-hour urine testing. Secondary outcomes will evaluate other urinary parameters and adverse events related to the interventions. Aim 2 will evaluate adverse effects from selective and empiric strategies and assess patient adherence. The contribution of the proposed research is expected to be identifying what preventative strategies work best among kidney stone patients, who are all at risk for kidney stone recurrence.