Introduction: It has been reported that particular subtypes of DR4 may contribute to IDDM susceptibility. Twenty-four different alleles (DRB1 * 0401-0424) encoding the b chain of the serological defined DR4 specificity, can be identified at the genomic level. Some studies have shown that DRB1 * 0401, * 0402 and * 0405 are associated with IDDM susceptibility whereas DRB1 * 0403 and * 0404 are found with decreased frequency in IDDM patients compared with healthy controls.Materials and Methods: In order to investigate the relative contribution of different DRB1 * 04 subtypes in IDDM predisposition we have studied 65 IDDM Croatian patients for DRB1, DQA1 and DQB1 polymorphism using PCR-SSO genomic typing. One hundred fifteen healthy individuals served as a control group.Results: Among 65 tested patients 35 were found to be DRB1 * 04 positive (53.8%) while in the control group the frequency of DRB1 * 04 alleles was 24.3%. The observed increase is highly statistically significant that is in concordance with results in other European populations. DRB1 * 04 subtyping did not reveal statistically significant difference between both tested groups. Analysis of DQA1 and DQB1 frequencies revealed highly significant increase of DQA1 * 0301 and DQB1 * 0302 (p < 0.001) and slightly decrease of DQB1 * 0301 (p < 0.05).Conclusion: No DRB1 * 04 subtype is by itself significantly increased or decreased in our patient group. The observed increase of DQA1 * 0301 and DQB1 * 0302 alleles is due to linkage disequilibrium with DRB1 * 04.