The prevalence of complementary medicine in most industrialised countries is impressive and increasing. Discussions of the topic often focus on therapeutic approaches and neglect diagnostic methods specific for complementary medicine. The paper summarises the data available on such "alternative" diagnostics. Scientific evaluations of these are scant, and most techniques have never been properly validated. The ones that have can be demonstrated to be not reproducible, sensitive, or specific. The ones that have not should be regarded as such until shown otherwise by rigorous testing. Therefore it seems that "alternative" diagnostic methods may seriously threaten the safety and health of patients submitted to them. Orthodox doctors should be aware of the problem and inform their patients accordingly.