Latent autoimmune diabetes in adults (LADA) is identified by the presence of GAD65 autoantibodies in diabetic patients who do not require insulin treatment for at least six months after the diagnosis. Previous studies have shown that the risk for LADA, similarly to type 1 diabetes mellitus (T1DM), is increased in subjects carrying the HLA-DRB1*03-DQA1*0501-DQB1*0201 and/or HLA-DRB1*04-DQA1*0301-DQB1*0302 haplotypes. In the present study, we investigated the association between LADA and the CTLA-4 A/G polymorphism, another gene polymorphism associated with T1DM and other autoimmune diseases. The heterozygous A/G genotype was significantly more frequent among 80 LADA (69%) than among 85 healthy subjects of similar age and geographical provenience (47%) (OR = 2.47, corrected P = 0.023). Conversely, the homozygous A/A genotype was significantly less frequent in LADA subjects than in healthy controls (26% vs. 47%, OR = 0.4, corrected P = 0.028). The results of our study show that LADA is positively associated with the CTLA-4 A/G genotype, similarly to T1DM, thus providing further supporting evidence of the autoimmune origin of this form of diabetes mellitus of the adult.