The issue of adverse health effects of ambient air pollution has been extensively studied and reported worldwide over the past two decades. The urban area of Reno and Sparks in northern Nevada is one of two major urban centers in Nevada; the other is Las Vegas. The northern area, which has undergone a rapid population growth in the last decade, has special geographic characteristics and air pollution patterns. We conducted environmental epidemiological studies spanning the 1990s. This report summarizes the evidence and discusses the findings in relation to other studies. Ambient air pollution levels, even when below federal standards, have a marked potential to impact human health adversely. Air pollution was associated with (1) emergency room visits for asthma; (2) hospitalization for chronic obstructive pulmonary disease; (3) hospitalization for cardio-vascular disease; (4) elementary school absenteeism; and (5) low birth weight, preterm birth, and other adverse birth outcomes.