Genetic predisposition to the complex hereditary disease like osteoarthritis (OA) of the large joints (hip and knee) includes the interleukin-1 gene (IL-1) cluster on chromosome 2. Using a case–control study with 500 OA patients (240 knee and 260 hip OA patients, all with joint replacement), we analysed frequencies of IL-1 gene cluster polymorphisms in Croatian Caucasian population. The control samples came from 531 healthy individuals including blood donors. We genotyped two single nucleotide polymorphisms in the IL-1 gene locus at IL-1A (−889, C>T, rs1800587) and IL-1B (+3594, C>T, rs1143634) and compared their frequencies between patients and controls. We predicted haplotypes by combining current data with our previous results on gene polymorphisms (IL-1B, rs16944 and the IL-1 receptor antagonist gene [IL-1RN] variable number tandem repeat [VNTR]) for the same population. Haplotype analyses revealed gender disparities and showed that women carriers of the 1-2-1-1 haplotype [IL-1A(rs1800587) – IL-1B(rs1143634) – IL-1B(rs16944) – IL-1RN(VNTR)] had sixfold lower risk to develop knee OA. However, carriers of the 1-1-1-2 haplotype of both sexes had over twofold higher predisposition to hip OA. Our results differ from some earlier studies in Caucasian subpopulations, which may be due to the fact that this is the first study to separate genders in assessing the IL-1-locus genetic risk of OA. The results suggest that inflammatory mediators like IL-1 might be implicated in the pathogenesis of primary OA in large joints and that as yet unidentified gender-specific factors exist in a Croatian Caucasian population.