There is increasing evidence implicating genetic factors in the susceptibility to diabetic microvascular complications. Recent studies suggest that increased expression of the cytokine vascular endothelial growth factor (VEGF) may play a role in the pathogenesis of diabetic complications. A number of polymorphisms in the promoter region of the VEGF gene have been identified. The aim was to investigate whether an 18 base pair (bp) deletion (D)/insertion (I) polymorphism at position -2549 in the promoter region of the VEGF gene is associated with the susceptibility to diabetic microvascular complications. Two hundred and thirty-two patients with type 1 diabetes mellitus (T1DM) and 141 normal healthy controls were studied. The D/D genotype was significantly increased in those patients with nephropathy (n=102) compared to those with no complications after 20 years duration of diabetes (uncomplicated, n=66) (40.2% vs. 22.7%, respectively, chi(2)=5.5, P<.05). The combination of polymorphisms of VEGF together with the aldose reductase (ALR2) gene showed that in the nephropaths, 8 of the 83 subjects had the VEGF I allele together with the Z+2 5'ALR2 allele compared with 27 of the 62 uncomplicated patients (chi(2)=26.7, P<.00001). The functional role of the D/I polymorphism was examined by cloning the region into a luciferase reporter assay system and transient transfection into HepG2 cells. The construct containing the 18 bp deletion had a 1.95-fold increase in transcriptional activity compared with its counterpart that had the insert (P<.01). These results suggest that polymorphisms in the promoter region of the VEGF gene together with the ALR2 may be associated with the pathogenesis of diabetic nephropathy.