Natural ventilation is the driving of outdoor air by natural forces such as winds and thermal buoyancy through purpose-built openings in buildings. Only until recently when air conditioning is adopted as a way of life, hospitals uses natural ventilation. Recently the WHO released a guideline "Natural Ventilation for Infection Control in Health-care Settings" that can be downloaded in the WHO website. The salient point to appreciate is that natural ventilation is effective even for the isolation of infections which are airborne. A summary of the guideline will be presented especially the basis for using it in the isolation of airborne transmitted infections. This will include the general principles of natural ventilation and to compare it with mechanical ventilation. The role of ventilation in the prevention of infections will also be discussed. Data to show that natural ventilation can be effective even in the prevention of pulmonary tuberculosis will be made available. Finally a brief summary on design and operations will be presented.