Few studies have been done on indoor air pollution in areas of extreme poverty in developing countries. In such countries, for economic reasons, people use solid fuel for cooking and heating fuels which by incomplete combustion generate high levels of toxic pollutants. These represent an important risk factor for human health. We have investigated the levels of carbon monoxide (CO), sulphur dioxide (SO2), respirable particulate matter (PM10 ), polycyclic aromatic hydrocarbons (PAHs) and mutagenicity in the PM5 fraction, as well as temperature and humidity, in the interior of 24 houses in La Pintana, Santiago. In addition, we have conducted a survey about symptoms, signs and respiratory diseases possibly associated with socio-economic factors in the area. The survey showed that in children younger than 2 years, most respiratory diseases occur during winter (75%), the most frequent complaint being bronchitis (62%) and obstructive bronchitis (50%). The higher pollutant concentrations were observed during heating hours, in houses that used coal (mean PM10 250 µg·m–3, CO 42 ppm, SO2 192 ppb) or firewood (mean PM10 489 µg·m–3, CO 57 ppm, SO2 295 ppb). PAHs were detected in all houses and we concluded that they came from inside the house and not from outdoor infiltration. Coal, firewood and cigarette smoke were important sources of mutagenic and carcinogenic PAHs, whereas kerosene and gas contributed mainly to the non-carcinogenic PAH fraction. In the houses studied, the population was exposed to levels of toxic pollutants that are much higher than those found outdoors in the highly polluted city of Santiago. In addition, overcrowding, excessive indoor humidity, very low indoor temperatures when the heating system was turned off, the presence of domestic animals, cats and dogs indoors and general lack of hygiene (with attendant bacteria and fungi) are risk factors to explain the high incidence of respiratory diseases in children.