The major histocompatibility complex region has been suggested to play an important role in the development of autoimmune thyroid disease (AITD). In this study, we investigated the associations of human leukocyte antigen (HLA) alleles and amino acid variants of HLA with early-onset AITD. HLA class I and class II genes were analyzed in 116 Korean children with AITDs (Graves’ disease [GD]: 71, Hashimoto’s disease [HD]: 45) and 142 healthy controls. HLA-B*46:01 (OR = 3.96, Pc = 0.008), -C*01:02 (OR = 2.51 Pc = 0.04), -DPB1*02:02 (OR = 3.99, Pc = 0.04), and -DPB1*05:01 (OR = 4.6, Pc = 0.003) were significantly associated with GD, and HLA-A*02:07 (OR = 4.68, Pc = 0.045) and -DPB1*02:02 (OR = 6.57, Pc = 0.0001) with HD. The frequency of HLA-DPB1*05:01 was significantly higher in GD patients than in HD patients ( Pc = 0.0005). Furthermore, differences were found between patients with Thyroid associated ophthalmopathy (TAO) and those without TAO in the distribution of HLA-B*54:01 (8.6% vs. 30.6%, P = 0.04) and -C*03:03 (37.1% vs. 11.1%, P = 0.02). In the analysis of amino acid variants of HLA molecules, both Leu35 (OR = 23.38, P = 0.0002) and Glu55 (OR = 23.38, P = 0.0002) of HLA-DPB1 were strongly associated with GD and showed different distributions between GD and HD ( P = 0.001). Our results suggest that HLA alleles, especially amino-acid signatures of the HLA-DP β chain, might contribute to the molecular pathogenesis of early-onset AITD.