Outdoor air pollution is a major determinant of health worldwide. The greatest public health effects are from increased mortality in adults. However, both PM and O3 also cause a wide range of other, less serious, health outcomes; and there are effects on mortality and morbidity of other pollutants also, e.g. nitrogen dioxide (NO2) and sulphur dioxide (SO2). These adverse health effects have economic consequences; OECD (2014) suggests that the social costs of the health impact of outdoor air pollution in OECD countries, China and India was approximately USD 1.7 trillion and USD 1.9 trillion, respectively, in 2010. However, the study highlights that though the social costs of premature mortality account for the majority of these totals, the social costs of morbidity remain poorly estimated. The objective of this paper is to inform the development of improved estimates of the social costs of human morbidity impacts resulting from outdoor air pollution in two components; namely to develop a core set of pollutant-health end-points to be covered when estimating the costs of morbidity, and to review current estimates of the cost of morbidity from air pollution.