Summary Recently published genetic studies in psoriasis, inflammatory bowel disease, and ankylosing spondylitis identified significant associations with IL12B and IL23R polymorphisms. An important role for the IL-12/IL-23 pathway in multiple sclerosis (MS) is supported by immunologic studies in patients and animal models. To determine whether IL12B/IL23R disease-associated polymorphisms play a role in susceptibility to MS, we genotyped 910 MS-nuclear families, totaling 3132 individuals. Family-based association analysis was performed. There was no evidence of transmission distortion of any of the tested alleles in this data set.