In recent years, poor indoor climate has increasingly been seen as the cause of health problems for building occupants. Today, there is good evidence in some areas why such problems arise. Unhealthy substances given off by various building materials, the existence of mould and general air pollution are the main causes. In general, the most important way to remedy the problem is improved ventilation. Poor upkeep and maintenance have led to a decline in the performance of existing ventilation systems. Briefly this is why the Swedish Parliament and Government decided, in complete unanimity, to introduce regulations on compulsory inspection of ventilation systems. The National Board of Housing, Building and Planning has issued the general guidelines about performance checks on ventilation systems which are presented briefly in this article.