© 2016, Turkish Journal of Pediatrics. All rights reserved.We have conducted this study for the purposes of demonstrating the spectrum of mutations and of identifying their effects on the phenotype, with a particular focus on the clinical course, prognosis and response to treatment. A total of 25 patients from 20 families, who have been treated and followed up after being diagnosed with cystinosis. Nine patients were identified with mutations of homozygous c.451A>G, 7 patients with homozygous c.681G>A, 6 patients with homozygous c.834_842del, 2 patients with homozygous c.18_21delGACT and 1 patient with compound heterozygous for c.451A>G/ c.1015G>A. The c.834_842del mutation identified in six patients from four families has not been previously identified. Progression to renal failure occurred earlier in the patients identified with the new mutation, despite treatment. Larger patient series are required to demonstrate the genotypic properties of the patients with cystinosis and their relationship with the clinical course.