Objective: Osteoporosis and obesity are complex diseases with a strong genetic component. Bone mineral density (BMD) and body mass index (BMI) linkage studies identified a locus at 1q21-23, where the interleukin-6 receptor (IL6R) gene is located. The IL6R and the gp130 receptors are the mediators of IL6 action. Serum levels of IL6 and sIL6R (the soluble form of IL6R) are higher in several diseases such as osteoporosis or obesity. Variants at IL6R have been associated with BMI and obesity. However, IL6R is an as-yet-unexplored osteoporosis candidate gene. Design: In the present study we analysed two polymorphisms in the IL6R promoter, - 1435 C/T (rs3887104) and -208 G/A (rs4845617), and the Asp358Ala polymorphism (rs8192284), in relation to both BMD and BMI in a cohort of 559 postmenopausal Spanish women. Results: The promoter polymorphisms, -1435 C/T and -208 G/A were associated with femoral neck (FN) BMD (P=0.011 and P=0.025 respectively). The C-A and T-G promoter haplotypes were also associated with FN BMD. Additionally, the Asp358Ala variant was associated with lumbar spine BMD (P=0.038). Finally, the -208 G/A polymorphism and the C-G and C-A haplotypes were associated with BMI and obesity, where GG was the risk genotype (P=0.033 for BMI; P=0.010 for obesity). Conclusion: These data suggest that variants in the IL6R gene are not only involved in the determination of BMI but also relevant for the determination of BMD. The IL6R gene may belong to the growing list of genes known to be involved in both phenotypes. © 2007 Society of the European Journal of Endocrinology.