We reviewed the main epidemiological studies that evaluate the respiratory effects of indoor air pollutants quantitatively in industrialised countries. Consistent results support short-term (aggravation) and, although more rarely, long-term (prevalence augmentation) effects on asthma, chronic bronchitis and chronic obstructive pulmonary disease (COPD) in indoor settings with poor air quality. Environmental tobacco smoke is one of the most important risks for respiratory symptoms and diseases worldwide. The evidence is also reliable for indoor nitrogen dioxide and particulate matter, which have been associated with asthma, bronchitis and COPD. Whereas formaldehyde and volatile organic compounds seem to be the main pollutants in indoor settings, relevant papers on their respiratory effects are still scarce, and limited to asthma and bronchitis. Moulds have been associated with an increased risk of asthma and COPD. Contradictory results have been found between endotoxins and asthma. The role of phthalates, persistent organic pollutants and flame retardants in respiratory diseases remains to be established. Results from rural areas of industrialised countries indicate that exposure to some indoor bio-contaminants might be protective in early life, while it is associated with adverse respiratory adverse effects in adulthood. Studies focusing on indoor air pollutants should be developed to better understand their involvement in the inception and aggravation of respiratory diseases.