As ethical banks have developed from niche players to a serious competition for traditional banks, supposedly ethical banks and even traditional banks use the term ethical bank in order to sell bank services under the cloak of sustainable and ethically correct business conduct.Therefore, the aim of this research is to make truly ethical banks distinguishable from traditional banks by investigating, analyzing and determining principles, ethical banks have to fulfill or refrain from in order to call themselves truly ethical. Based on academic research results, a web-based survey identifies the bank customer's attitude towards sustainability, ethics, and their banking, and the ethical attitude towards the nine areas of business, banks may be confronted with. The survey results build the basis for a list of positive and negative ethical guiding principles which should serve as a general standard for ethical banks.Nevertheless, the ethical guiding principles need to be continuously reviewed and validated as a consequence of the ever-changing environmental, social and legal environment. In the case of its direct implementation, a control mechanism within or outside the bank must monitor and ensure compliance with these principles.