The events after the exposure HIV virus follow a reasonably predictable chronological order. Various states proposed in the natural history of HIV infections are as follows: 1. Acute HIV infection: this stage has an infectious mononucleosis like syndrome that develops 3weeks to 3 months after initial exposure to HIV. CD+4 counts are transiently depressed and antibody tests are negative. HIV PCR is the most definitive test. 2. Early asymptomatic infection: patient remained asymptomatic but there was progressive derangement of immune system approximately 50% of patients developed diffuse enlargement of lymph nodes. CD4 count in this stage is more than 500/ml. 3. Late asymptomatic: viral replication increases and more CD4 and CD8 cells are destroyed resulting in decline in immune competence. CD4 count is between 200–500/ml. Symptomatic infections: constitutional symptoms associated with HIV include malaise, night sweats. Weight loss and diarrhea lasting 1 month, fever lasting at least 1 month. Between the acquisition of HIV infection and seroconversion is called the Window period which is usually 6 to 12 weeks.