Cancer awareness among adolescents has a critical role in future cancer prevalence, therapy and early diagnosis. The aim of the study was to determine the knowledge level of adolescents about cancer and it's symptoms. The 9-12th class students of two high schools were involved in the study. After getting informed consent 1311 students were asked to answer a questionnaire form. The mean age was 16.3 +/- 1.12. The cases were grouped as Group 1 (adolescents without family members with cancer) and Group 2 (the cases that had family members with cancer). The awareness rates for all of nine common cancer signs were significantly higher in adolescents that had family members with cancer. The presence of a family member with cancer increased the rates of being aware but the increased awareness in that group did not change the attitudes towards possible presence of cancer symptoms.