NIDDM is one of the most common forms of diabetes. The diagnosis is based on WHO classification, which is a clinical classification and misses the autoimmune diabetes in adults. Therefore, among the clinically diagnosed NIDDM cases, there can be a certain number of patients with latent autoimmune diabetes in adults (LADA). The MICA gene is located in the MHC class I region and is expressed by monocytes, keratinocytes, and endothelial cells. Sequence determination of the MICA gene identifies trinucleotide repeat (GCT) microsatellite polymorphism, which identifies 5 alleles with 4, 5, 6, and 9 repetitions of GCT (A4, A5, A6, and A9) or 5 repetitions of GCT with 1 additional G insertion for allele A5.1. From our previous studies, we have shown that microsatellite allele A5 of MICA is associated with IDDM. The aim of this study was to test the hypothesis that certain MICA alleles are associated with LADA among clinically diagnosed NIDDM. Out of 100 clinically diagnosed NIDDM patients, 49 tested positive for GAD65 and IA-2 antibodies by use of 35S RIA. Samples from these 49 patients and 96 healthy controls were analyzed for MICA by PCR amplification, and fragment sizes were determined in an ABI prism DNA sequencer. Our results show that MICA allele A5.1 is significantly increased in antibody-positive (GAD65 or IA-2) NIDDM patients [35/49 (72%)] when compared to healthy controls [22/96 (23%)] (OR = 8.4; P < 0.0001). However, we do not see any association with each of the antibodies separately. From our study, we conclude that (a) MICA allele A5.1 is associated with LADA and (b) MICA may play an important role in the etiopathogenesis of LADA.