Our studies on pathology of AIDS point to four major conclusions. 1) The brain is often directly affected by the HIV infection (with the characteristics of subacute microglial encephalitis with pathognomonic multinucleated giant cells) and then by opportunistic infections such as Cytomegalovirus, Herpes-virus, Papova-virus JC (with progressive multifocal leucoencephalopathy), Mycobacterium tuberculosis, Toxoplasma gondii, Cryptococcus neoformans, Candida albicans and Aspergillus fumigatus; opportunistic neoplasms (i.e. B cell lymphoma mostly pluricentric) could also developed. 2) The heart is frequently involved as well; perivascular sclerosis and myocytolysis are the hallmarks of a peculiar cardiomyopathy. 3) In the lung viral, bacterial, fungal an protozoan severe infections are frequently present: common are those caused by Cytomegalovirus and Pneumocystis carinii. Frequently thin fibrotic interalveolar septa are observed (with consequent alteration of hematosis). 4) Adrenal (most frequently) and pituitary may display necrotic-hemorragic areas (in adrenals chiefly due to Cytomegalovirus). These may be extensive enough to explain the occurrence of clinical syndromes of endocrine insufficiency.