[Show abstract][Hide abstract] ABSTRACT: Beta-thalassemia is the most common hereditary disease in Iran. More than two million carriers of beta-thalassemia live in Iran. Since the Iranian population is a mixture of different ethnic groups, it is necessary to determine the frequency and distribution of mutations in the different parts of the country. For this purpose, we divided Iran in to eight different regions according to the geographic and ethnic distribution of the population. Over a 10-year period 1,217 beta-thalassemia chromosomes of 164 affected patients and 889 unrelated carriers were studied using the amplification refractory mutation system-polymerase chain reaction technique. We detected 81% beta-thalassemia mutations in the studied chromosomes. IVS-II-I (G --> A) was the predominant mutation found in our study (34%). Its relative frequency in the north was much higher than other regions, and it lessened toward the south, where the IVS-I-5 (G --> C) mutation was more common. IVS-I-5 (G --> C) (7.55%), codons 8/9 (+ G) (4.76%), and IVS-I-110 (G --> A) (4.76%) were the other most common mutations. The results presented here can be used as a basis of prenatal diagnosis of beta-thalassemia in different regions of Iran.