The primary complex generally exists singly and only occasionally in multiple units. In overwhelming majority of cases primary complex occurs in the lungs, called as Ghon's focus. It generally occurs in the subpleural region of any lobe. Mostly hilar and inter-pleural lymph nodes are involved to form the primary complex. Sometimes the primary complex (Ghon's complex) can be seen radiographically, mostly in the lower and middle lobes, and comprises the primary lesion, hilar lymphadenopathy plus/minus a lymphangitic track. Later on, the primary lesion tends to become calcified, and can be identified on the chest x-rays for decades.