AIDS patients experience immune system failure as their T-helper cells are continually depleted. This causes AIDS patients to develop opportunistic infections in their weakened states. Patients eventually succumb to these infections that a healthy individual would otherwise be able to fight off. This then means that people do not actually die of 'AIDS' they instead die of whatever infection takes over their body which their compromised system is unable to fight off.
How is HIV transmitted?
Source: Biology of Women, Ethel Sloane