Exposure to indoor radon and suspended particulate matter (SPM) is considered a high risk in lung cancer aetiology. In this paper indoor radon and SPM concentration measurements and their correlations, associated with lung cancer cases are given. Mexico City suffers high concentration of SPM as well as other photochemical pollutants such as ozone. During the last decade in Mexico City, radon and SPM have been monitored. The indoor radon measurements were done using the Nuclear Track Methodology, basically the close-end-cup device with polyallyldiglycol carbonate as detector material, followed of an established chemical etching protocol, and automatic digital image analyzer system for counting. SPM size and concentration were obtained from monitoring stations located along the city. The results show that the central–north part of Mexico City has a large concentration of SPM and the vulnerable population (older than 65 years and younger than 14 years) is located essentially in the same region. In this area, a large number of lung cancer cases were found, even if indoor radon levels were below the recommended limits.