This study aims to determine the effect of vitamin D replacement on patients presenting to a tertiary stone clinic in terms of changes in 24-hour urine collection parameters and secondary stone formation. Eighty- six eligible patients with 25-(OH)D deficiency or insufficiency (defined as serum level <72 nmol/L) with history of calcareous urolithiasis and urinary calcium excretion <7.5 mmol/day will be included in the study.