Background : Discovering the etiology of diseases especially cancers are research priority. There are controversies around the role of absence of GSTM1 and increased risk of development of several malignancies. Thus, the present study was conducted to determine the association between its genotypes and colon cancer in Namazi hospital in Shiraz.

Materials and methods: For this case-control study, the polymorphism of GSTM1 was determined using PCR technique in 38 patients with colon cancer and 76 control subjects. Chi-square and odd’s ratio were used for data analysis.

Results : The frequency of null genotype was 32.9% and 50% in controls and cases, respectively (p<0.05). There exists a statistically significant association between null genotype and colon cancer among individuals older than 59 years old (p<0.02).

Conclusion : There is a close association between GSTM1 null genotype, especially in older population, and development of colon cancer.