Objectives: To verify whether the concentrations of arsenic (As) and its compounds in the air (referred to here as arsenic concentrations) affect the standardized mortality ratio (SMR) associated with lung cancer. Methods: Using monitoring survey data on arsenic concentrations published by the Ministry of the Environment, we classified the municipalities for which arsenic concentrations were measured (measured municipalities) into ten groups according to the average arsenic concentration. We then determined the SMR of lung cancer, stomach cancer, pneumonia, cerebrovascular disease and cardiac disease for each group using socio-demographic data, such as the national census and demographic trends. The relationships between these factors were compared and investigated by statistical means. Results: No effect of arsenic concentrations on stomach cancer, cerebrovascular disease or cardiac disease was observed, and while significant differences in pneumonia were observed among several of the male subjects, there were no significant effects of arsenic concentration. However, lung cancer and arsenic concentration showed a significantly positive correlation for both males and females (males: Spearman r = 0.709, P &lt
0.05
females: Spearman r = 0.758, P &lt
0.05). The probability of type α error was less than 5% in areas with more than 1.77 ng As/m3 (71st percentile) and less than 1% in areas with more than 2.70 ng As/m3 (91st percentile). These results confirm that the SMR of lung cancer tends to be higher than the national average in areas of higher arsenic concentrations. Conclusions: The SMR of lung cancer is significantly higher in areas with arsenic concentrations of 1.77 ng/m3 or more. © 2008 The Japanese Society for Hygiene.