Abstract
Ethical core issues in research with human subjects are related to informed consent and risk-benefit assessment. This is valid for all types of studies. However, there has been much greater focus of ethical considerations on controlled clinical trials than on naturalistic trials, probably because the former are interventional in nature and may have unknown and perhaps severe somatic risks, whereas naturalistic studies seem not to intervene but only to observe, and therefore are assumed to have fewer or almost no risks. However, there are also ethical implications in naturalistic trials, although their weight is differently accentuated, more with potential, more with potential psychological burdens of the observational procedures and more with potential physical risks in interventional trials. This will be elaborated with examples of placebo-controlled trials and of incidental findings in screenings, of marketing influences on observational studies, and of psychological burdens by survey interviews. The ethical implications will be analyzed within a more general framework. Finally, recommendations will be offered.