The heterozygous combination of DQA1*03-DQB1*0302 (DQ8) and DQA1*05-DQB1*0201 (DQ2) confers the highest known HLA-DQ-linked risk for type 1 diabetes, suggesting a role for transcomplementation. The trans-heterodimer encoded by DQA1*03 and DQB1*02 is also rarely observed in cis in whites. Islet antibody-positive diabetic patients (P; n = 2,238) and control subjects (C; n = 2,223) of white descent were genotyped by a HLA-DQA1-DQB1 dot-blot method. The presence of the DQA1*03-DQB1*02 haplotype was observed in 22 patients (1%) versus 6 controls (0.3%) (odds ratio [OR] = 3.7, p = 0.005). It was more prevalent in whites of Northern African descent, but both in European (n = 3,813) and in Northern African whites (n = 648), the DQA1*03-DQB1*02 haplotype tended to be associated with diabetes (respectively, P 0.3% vs. C 0.03%, OR = 12.2, p = 0.005; and P 2.1% vs. C 0.6%, OR = 3.8, p = 0.03). DRB1 typing revealed that DQA1*03-DQB1*02 is usually associated with the DRB1*0405 risk allele in European patients and with DRB1*0405, DRB1*07 and DRB1*09 in Northern African whites. Like in DQ2/DQ8-positive patients, the presence of DQA1*03-DQB1*02 is preferentially associated with younger age at clinical onset than in other genotypes, but unlike in subjects carrying DQ2/DQ8, earlier clinical manifestation was mostly restricted to male subjects, often carrying DR3 and/or DQB1*02 on the other chromosome. These results are compatible with an effect of cis-encoded heterodimers or with previously suggested interactions of X-linked genetic factors with (DR3-)DQB1*02 haplotypes.