A systematic literature review suggests that particulate air pollution is associated with daily admissions for both respiratory and cardiac diseases in people aged > 65 yrs. A model of acute effects is proposed which shows how admissions can be brought forward by a relatively short period of time as well as events being added that would not have happened at all except for air pollution. A model of the effects of air pollution on chronic disease is proposed that provides the background of long-term vulnerability upon which the increased short-term vulnerability is superimposed. A study of daily hospital admissions in London shows that for respiratory disease the relative risks of admission associated with particles reduce with increasing age, while for cardiac disease, there is no trend. When the attributable risk is estimated using baseline admission rates for respiratory disease, it is children who have the highest attributable risk, followed by the elderly. For cardiac disease there is a steep increase in attributable risk with age, reflecting the dominant influence of baseline risks. The attributable risk for cardiovascular disease in the elderly is considerably greater than for respiratory disease, due to higher baseline admission rates.