Background & Aims: Urinary tract infection (UTI) is one of the most frequently acquired bacterial infections caused by a large genetically heterogeneous group of Escherichia coli which are called uropathogenic E. coli (UPEC). Cystitis and pyelonephritis are two most common symptoms seen in patients with UTI. The genetic diversity of this organism has hampered the identification of UTI strains and it is unclear whether all UPEC isolates are capable of causing both cystitis and pyelonephritis. Therefore, Careful selection of appropriate genotyping methods is mandatory. The most popular method is Pulsed Field Gel Electrophoresis (PFGE) that is used in the present study to evaluate the genetic patterns of UPEC. Methods: In this cross-sectional study a total of 90 E. coli strains consisting of 48 isolates causing pyelonephritis and 42 isolates causing cystitis in children were analyzed by PFGE and their corresponding patterns were compared. Results: Sixty six PFGE profiles were obtained from the genome of E. coli strains by this genotyping method. Most strains exhibited twelve and thirteen bands and the patterns with eight or nineteen bands had the lowest rate. Genome size of strains was between 1610-4170 kbp. Conclusion: According to these results, it can be suggested that in some cases the strains causing pyelonephritis or cystitis have common patterns and different clinical symptoms could be attributed to different gene factors.