Aims/hypothesis: We examined whether the non-HLA susceptibility locus ERBB3/IKZF4 influences progression of type 1 diabetes stage specifically according to sex. Methods: SNPs of ERBB3 (rs2292239 T/G) and IKZF4 (rs1701704 G/T) were screened by allelic discrimination quantitative PCR assay in first-degree relatives of type 1 diabetes patients who had developed at least one circulating autoantibody. The effect of ERBB3/IKZF4 genotypes and sex, on the progression of single autoantibody positivity to multiple autoantibody positivity and from multiple autoantibody positivity to diabetes, was studied by Kaplan–Meier analysis and multivariate Cox regression. Results: In the cohort of autoantibody-positive first-degree relatives, the risk allele frequencies for ERBB3 rs2292239 (T) and IKZF4 rs1701704 (G) were increased. There was a significant male excess at the stage of multiple autoantibody positivity (p = 0.021). In Kaplan–Meier survival analysis, progression from single to multiple antibody positivity was delayed in female participants with genotype ERBB3 GG (p = 0.018, vs ERBB3 TG+TT) or IKZF4 TT (p = 0.023, vs IKZF4 GT+GG), but not in male participants. In multivariate Cox regression models, the interaction effects between female sex and ERBB3 GG (p = 0.012; HR = 0.305 [95% CI 0.120, 0.773]) or between female sex and IKZF4 TT (p = 0.011; HR = 0.329 [95% CI 0.140, 0.777]) emerged as potential determinants of delayed progression to multiple autoantibodies. The progression from multiple autoantibody positivity to type 1 diabetes appeared not to be influenced by ERBB3/IKZF4. Conclusions/interpretation: In siblings and offspring of type 1 diabetes patients, polymorphism in region ERBB3/IKZF4 may affect disease progression at the level of epitope spreading in female individuals. Our findings suggest that interaction between sex and ERBB3/IKZF4 may contribute to the post-pubertal male excess in type 1 diabetes. Graphical abstract: [Figure not available: see fulltext.].