The present study aimed to determine awareness of Tehran residents of seven warning signs of cancer, and application of protective measures against cancer. 2500 residents of Tehran were selected through systematic cluster random sampling. Data collection tool consisted of a questionnaire, comprising 3 sections of demographic details, awareness of warning signs of cancer, and application of protective measures against cancer. Validity and reliability of the questionnaire were determined through content validity and Cronbach’s alpha. Data were collected once and in-person, and were analyzed with SPSS-11.5 software using Chi-square test. As for favorability of their status, 80%-100% was considered favorable, 60%-79.9% relatively favorable, and 0-59.9% unfavorable. Study results revealed the majority of Tehran residents (66.6%) had an unfavorable status in terms of awareness of warning signs of cancer, and only 9% were in a favorable status. Most participating Tehran residents (78.7%) were in an unfavorable status in terms of applying protective measures against cancer, and only 7.6% had favorable status. A significant relationship was observed between awareness of warning signs and protective measures against cancer. Therefore, it is recommended to increase people’s awareness of cancer prevention.