Studies of the health effects of biomass smoke exposure in developing countries are being reviewed, but where their availability is limited, studies of wood smoke, environmental tobacco smoke (ETS) and ambient (outdoor) pollution from developed countries are also included. There is now consistent evidence that biomass smoke exposure increases the risk of childhood acute respiratory infections, particularly pneumonia, and probably otitis media. An association between smoke exposure with chronic bronchitis (assessed by symptoms) and chronic obstructive pulmonary disease (assessed clinically and by spirometry) is well established, in particular among women. In line with findings for ETS, there is emerging evidence that exposure during pregnancy reduces birth weight, possibly mediated through carbon monoxide. Infant and perinatal mortality may also be increased. Furthermore, biomass smoke exposure is likely to exacerbate asthma, although the evidence is limited and conflicting. A number of studies have also shown evidence of an increased risk of tuberculosis. Finally, human and animal studies suggest an increased risk of cataract, which is supported by evidence from studies on ETS.