Type 1 diabetes is an autoimmune disease that is caused by destruction of pancreatic β-cells. Type 1 diabetes is a heterogenic disease with environmental factors as well as genetic components. It is well established that environmental factors can exert their effects only on genetically susceptible patients. There is increasing evidence that genes outside the major histocompatibility complex (MHC) region contribute to the pathogenesis of type 1 diabetes. Cytokines, due to their role in immune regulation, seem to play a crucial role in the pathogenesis of the disease. In order to investigate the immunosuppressive action of transforming growth factor-β1 (TGF-β1) in type 1 diabetes, 388 patients with type 1 diabetes and 229 normal controls were genotyped for the TGF-β1 T (29) C gene polymorphism. The TGF-β1 T (29) C gene polymorphism was amplifi ed using ARMS-PCR. Practical part of this work was conducted in Molecular Medicine Research Group, Peninsula Medical School, Plymouth, UK. However, statistical analyses were performed in Department of pathology, Salmaniya Medical Complex, Kingdom of Bahrain. From three different genotypes of TT, TC, and CC of the TGF-β1 T (29) C, the TC frequency increased in patients with type 1 diabetes compared to normal controls, P value = 0.00001. The TC frequency was signifi cantly higher in patients with diabetic nephropathy (DN) in comparison with diabetic control, P value = 0.007. Further, the CC frequency was signifi cantly less in patients compared to healthy normal control subjects, P value = 0.005. Genetic variation at the TGF-β1 gene polymorphism T (29) C located in codon 10 is likely to confer signifi cant susceptibility to advanced DN in patients with T1D. This is a small case-control study in Caucasians to investigate the role of the TGF-β1 gene polymorphism T (29) C located in codon 10 in the genetic predisposition to T1D and DN. To our knowledge, this is the fi rst genetic report highlighting the dual effects of TGF-β1 in the onset of T1D as well as type 1 DN and can be a good model for extensive studies.