M467T mutation (exon 8) in rBAT gene is found to be the most common mutation in cystinuria type I patients. In our series consisting of 24 patients, the allele frequency of the M467T mutation was 8.3 percent (4/48). The second most frequent mutation at the same nucleotide position was M467K, with an allele frequency of 4.2 percent (2/48). The polymorphism which is found in linkage disequilibrium with the M467T is 231T/A (exon 1). We also found that 231T/A was associated with the M467T mutation in our series.