Plasma leakage is the leakage of protein rich fluid component of blood from the blood vessels in to the surrounding tissues. Since the size of red blood cells is too large as compared to other components of plasma therefore, they don’t leak through the blood vessel. This results in increase in hematocrit, called hemoconcentration. Patients who present with fever show progressive increase in hematocrit level. It usually begins after 3-4 days of onset of fever. But those patients who reveal severe plasma leakage show increase in hemoconcentration by more than 20%. Plasma leakage is a very severe complication that marks the progress of dengue into severe dengue.