This paper reports on knowledge and behavior among Dutch adults (n = 1530) regarding early detection of cancer (passive detection, active detection and help-seeking behavior). Written questionnaires assessed knowledge of detection methods and cancer symptoms, symptom recognition, detection behaviors, and help-seeking behaviors. Respondents did not have much general knowledge of detection methods and cancer symptoms, but recognized most cancer symptoms. More women than men paid attention to cancer symptoms. For most symptoms, medical help would be sought within the appropriate time by the majority of the respondents. Principal component analyses revealed relations between symptoms pertaining to the 'interior' body and those pertaining to the 'exterior' body. Correlations between symptom recognition, detection behavior and help-seeking behavior were low. Differences in demographic groups and differences in knowledge and behavior require adaptation of future health education on early detection of cancer to different groups.