The question 'Does air pollution cause significant adverse effects in humans' misses the real health issue. The more appropriate question is: what role does air pollution play in causing, promoting, facilitating, and/or exacerbating the lung disease that is present in all adults. The present study is a first step in the direction of inventory, an assessment of pathologically overt injury to a key unit of the acinus, the centriacinar region (CAR). The lungs of 107 of 118 youths (14-25 years of age), who died in vehicular accidents or were homicide victims, were suitable for pathologic examination, and the extent and severity of disease was determined. Of the 107 youths, 29 (27%) had severe CAR disease as judged by scores of 5 or more (on a scale of 1-10) for both severity and extent. The high incidence and severity of CAR disease in youths is unprecedented and cannot be attributed to any single agent. The pathogenesis is undoubtedly multifactorial, with socioeconomic factor dominant, in particular a suboptimal level of health care, greater impact of respiratory tract infections, high levels of air pollution, and heavy smoking and some illicit drug use. Air pollution is highly suspect for a substantial contributory role.