A pilonidal sinus is a cavity in the subcutaneous tissue which is lined by granulation tissue, generally contains hair and communicates with the surface by a track which is usually lined by squamous epithelium continuous with epidermis. The etiological theories of pilonidal sinus are: Congenital & acquired. The first one: Sequestration dermoid cyst getting infected and ruptured leading to a sinus. This is no longer accepted since it does not date since birth. It’s not preceded by a cyst and is not lined by epithelium. Acquired Theory: The most accepted is an inclusion of loose hair under the skin due to continuous friction and negative pressure of area which may suck other hairs into the sinus. Pilonidal sinus occurs in young male more than female and is more in hirsute people.