CYLD (Ubiquitin carboxyl-terminal hydrolase) belongs to peptidase C19 family with 956 amino acids. It is a cytoplasmic protein with three cytoskeletal-associated protein-glycine-conserved (CAP-GLY) domains which function as a deubiquitinating enzyme which specifically cleaves 'Lys-63'-linked polyubiquitin chains and 1 ubiquitin-specific proteases (USP) domain. CYLD plays an important role in the regulation of pathways leading to NF-kappa-B activation, proliferation and differentiation. It also interacts with (via CAP-Gly domain) IKBKG/NEMO (via proline-rich C-terminal region). CYLD is important for the survival of immature natural killer cells whereas it is not required for the maturation of intrathymic natural killer cells. It is detected in fetal brain, testis and skeletal muscle, and at a lower level in adult brain, leukocytes, liver, heart, kidney, spleen, ovary and lung. Isoform 2 is found in all tissues except kidney. CYLD related diseases are multiple familial trichoepithelioma 1 and familial cylindromatosis.