AIDS-related illnesses are health conditions that occur in individuals with HIV infection, particularly when the immune system is severely weakened. HIV attacks the body's immune cells, making it difficult to fight off infections and diseases. Common AIDS-related illnesses include certain types of cancers, such as Kaposi's sarcoma, and opportunistic infections like pneumocystis pneumonia. These illnesses can be life-threatening and often indicate that a person has progressed to AIDS, the final stage of HIV infection. Early diagnosis and treatment of HIV can help prevent the progression to AIDS and reduce the risk of developing these serious health issues.