Objective: To determine the frequency of DYT1 mutation in Iranian patients affected withprimary dystonia.Materials and Methods: In this study, we investigated 60 patients with primary dystoniawho referred to the Tehran Medical Genetics Laboratory (TMGL) to determine thedeletional mutation of 904-906 del GAG in the DYT1 gene. DNA extracted from patients’peripheral blood was subjected to PCR-sequencing for exon 5 of the DYT1 gene. The collectionof samples was based on random sampling.Results: The deletional mutation of 904-906 del GAG in the DYT1 gene (15099 to 15101based on reference sequence: NG_008049.1) was identified in 11 patients (18.33%). Theaverage age of affected patients with this mutation was 13.64 ± 7.4 years.Conclusion: It can be concluded that the DYT1 deletional mutation of 904-906 del GAGhas a high frequency in Iranian patients in comparison with other non-Jewish populations.Therefore, this particular mutation may be the main representative of pathogenic DYT1gene for a large proportion of Iranian patients with primary dystonia