An insertion/deletion (I/D) polymorphism in the angiotensin-converting enzyme (ACE) gene has repeatedly been shown to be associated with ischaemic heart disease, but the association of this genetic marker with diabetic microangiopathy is controversial. To assess the association of the genotypes with the development of diabetic nephropathy or retinopathy, we performed a meta-analysis of data from the literature, using Mantel-Haenszel method followed by the Breslow-Day test for assessing homogeneity among data. In a total of 4773 diabetic patients from 18 studies with (n = 2495) and without (n = 2278) renal complications, the D allele was significantly associated with diabetic nephropathy (p < 0.0001) in a dominant model (summary odds ratio 1.32, 95% confidence interval: 1.15 to 1.51). There was no significant evidence against homogeneity of the odds ratios (chi(2) = 18.9, 20 df; p = 0.53). The association was significant both in non-insulin-dependent (p < 0.005) and in insulin-dependent diabetes mellitus (p < 0.05). Likewise, in a total of 2010 diabetic patients with (n = 1008) and without (n = 1002) retinopathy, there was no association of the I/D polymorphism with diabetic retinopathy. These data suggest that the ACE I/D polymorphism affects the risk for diabetic nephropathy, but not for diabetic retinopathy.