A national random sample of 855 Australian general practitioners was surveyed about their belief in the effectiveness of cancer screening tests in reducing premature mortality. Responses were then compared with scientific evidence of effectiveness for each test. 92% of respondents believed mammography to be effective compared with only 38% for faecal occult blood testing, despite comparable evidence of effectiveness from randomised controlled trials. Seven tests outranked their belief in faecal occult blood testing, despite weaker evidence. Further efforts are required to align general practitioners' beliefs better with the evidence.