A total of 576 Spanish RA patients from Northern Spain were genotyped for 6 well-known IL33-IL1RL1 polymorphisms (IL33 rs3939286, IL33 rs7025417, IL33 rs7044343, IL1RL1 rs2058660, IL1RL1 rs2310173 and IL1RL1 rs13015714) by TaqMan genotyping assay. Here, IL33 is linked to rheumatoid arthritis.