The present study was performed to determine what proportion of people in Sardinia with or without Crohn's disease were infected with Mycobacterium avium subspecies paratuberculosis and had a preponderance of allelic variants of Nod 2, an intracellular protein involved in Crohn's disease susceptibility. Genetic analysis of the alleles of the NOD 2/CARD 15 gene (ins C 3020, G 908 R, and R 702 W alleles), linked to susceptibility or genetic predisposition to Crohn's disease in humans, was carried out on specimens from 37 Crohn's disease patients and 34 patients without Crohn's disease. Our results show that more than 70 percent of people in Sardinia with Crohn's disease carry at least one of the susceptibility-associated NOD 2/CARD 15 alleles and were infected with Mycobacterium avium subspecies paratuberculosis.