The objective of this study was to determine the frequency of nephrocalcinosis and hypercalciuria in cystic fibrosis (CF) patients, and to search possible causes of this phenomenon. Forty-three CF children (24 boys, 19 girls; mean age 64.9 months, range 5 months-18 years) were included in this study. Plasma sodium, potassium, chloride, BUN, creatinine, calcium, phosphorus, magnesium, alkaline phosphatase; spot urine sodium, potassium, chloride, creatinine, calcium, magnesium; and serum 25-hydroxyvitamin-D levels were measured in all patients. Urine samples were examined for microscopic hematuria. Fractional sodium, potassium, chloride excretion and estimated glomerular filtration rate (GFR) were calculated. All patients underwent renal ultrasonography. Hypercalciuria, nephrocalcinosis and microscopic hematuria were detected in 15 patients (34.2%), 10 patients (23.2%) and two patients (5%), respectively. There was no significant but borderline correlation between 25-hydroxyvitamin-D levels and hypercalciuria (r: 0.308, p:0.05). There were no correlations between Shwachman clinical scoring system results and hypercalciuria (r: 0.221, p: 0.148) and age and hypercalciuria (r: -0.229, p: 0.135). Patients with chronic Pseudomonas colonization showed no hypercalciuria or nephrocalcinosis. There was no difference for plasma biochemical results, renal function tests, hypercalciuria and nephrocalcinosis between CF patients who had or had not experienced pseudo Bartter's syndrome (PBS) before. There was no relation between detected CF mutations of the patients and hypercalciuria and nephrocalcinosis. These results suggested that it is a primary abnormality of calcium metabolism in the kidney.