Interleukin (IL)-1 has been shown to induce peritoneal adhesions. We determined the IL-1 receptor antagonist (IL-1RN) genotype with respect to the two most common variant alleles IL-1RN*2 and IL-1RN*3 in Caucasian women with peritoneal adhesions. One hundred seven women with surgically verified peritoneal adhesions and 79 controls without peritoneal adhesions served as controls. Univariate analysis showed an increased risk for peritoneal adhesions for Caucasian women carrying the mutant IL-1RN*2 allele (OR: 2.1; 95% CI: 1.3-3.4; P = 0.004). Multiple logistic regression analysis demonstrated an increased risk for peritoneal adhesions, which is independent of previous abdominal surgery and endometriosis. Our data suggest that IL-1RN*2 allele carriers have an increased risk for adhesion formation.