The function of the Laccase domain-containing 1 (LACC1) gene is unknown, but genetic variation at this locus has been reported to consistently affect the risk of Crohn's disease (CD) and leprosy. Recently, a LACC1 missense mutation was found in patients suffering from monogenic forms of CD, but also systemic juvenile idiopathic arthritis. We tested the hypothesis that LACC1 single nucleotide polymorphisms (SNPs), in addition to CD, are associated with juvenile idiopathic arthritis (JIA, non-systemic), and another major form of inflammatory bowel disease, ulcerative colitis (UC). We selected 11 LACC1 tagging SNPs, and tested their effect on disease risk in 3855 Swedish individuals from three case-control cohorts of CD, UC and JIA. We detected false discovery rate corrected significant associations with individual markers in all three cohorts, thereby expanding previous results for CD also to UC and JIA. LACC1's link to several inflammatory diseases suggests a key role in the human immune system and justifies further characterization of its function(s).