Urolithiasis is a significant and a common health problem in children’s nephrology and urology. Taking into account the consequences, such as colic renal pain, recurrent urinary tract infection and renal failure, fast diagnosis and treatment of urolithiasis is needed. Hypercalciuria is the most common metabolic abnormality in patients with calcium kidney stones. Hypercalciuria may be caused by increased intestinal calcium absorption, decreased renal calcium reabsorption or hyperparathyroidism. A serum calcium level is steady and is regulated by the actions of parathyroid hormone, vitamin D3 and the opposing effect of calcitonin. We describe two clinical cases that demonstrate uncommon aetiology of urolithiasis: the male patient with recurrent urolithiasis caused by hyperparathyroidism due to parathyroid gland hyperplasia and the female patient with hypercalcaemia accompanied by urolithiasis and Williams syndrome suspicion. Hyperparathyroidism is characterised by high serum calcium level, hypercalciuria, elevated PTH and renal metabolite of vitamin D3 concentration. The clinical manifestation of Williams’ syndrome include distinct facial appearance associated with cardiovascular anomalies, intermittent hypercalcaemia and hypercalciuria, neurodevelopmental and gastrointestinal tract abnormalities. A characteristic behavioural profile, in children with Williams’ syndrome, is observed and called “cocktail party”.