Vitamin D and interleukin (IL)-1 have been suggested to function in the pathogenesis of type 1 diabetes mellitus (T1DM). Therefore, we examined the influence of gene polymorphisms in vitamin D receptor (VDR) and interleukin-1 receptor type I (IL-1-R1) on susceptibility to T1DM in the Dalmatian population of South Croatia. We genotyped 134 children with T1DM and 132 controls; for FokI polymorphism studies, we extended the control group to an additional 102 patients. The VDR gene polymorphism FokI displayed unequal distribution (P = 0.0049) between T1DM and control groups, with the ff genotype occurring more frequently in T1DM individuals whereas the VDR gene polymorphism Tru9I did not differ in frequency between studied groups. All tested polymorphisms of the IL-1-R1 gene [PstI, HinfI, and AluI (promoter region) and PstI-e (exon 1B region)] displayed no differences between cases and controls. Haplotype analysis of the VDR gene (FokI, BsmI, ApaI, TaqI, Tru9I) and of the IL-1-R1 gene (PstI, HinfI, AluI, PstI-e) found haplotypes VDR FbATu (P = 0.0388) and IL-1-R1 phap' (P = 0.0419) to be more frequent in T1DM patients whereas the BatU haplotype occurred more often in controls (P = 0.0064). Our findings indicate that the VDR FokI polymorphism and several VDR and IL-1-R1 haplotypes are associated with susceptibility to T1DM in the Dalmatian population.