This report provides information on indoor air quality and on associated potential risks in hospitals. Spread and persistence of microbial communities in hospital environments are of huge interest to public health. Hospitals are characterized by high infective risk, firstly cause of the compromised immunologic conditions of the patients that make them vulnerable to bacterial, viral, parasitological and fungal opportunistic infections. Evidence suggests that microbial agents spread through air, surfaces, aerosol and hands. If surfaces may act as a reservoir for some pathogens, hands are an important transmission route. Airborne and aerosolized waterborne microorganisms are taken into consideration, and their presence into the hospital environments is reviewed.