Conducting ethically sound research is a fundamental principle of scientific inquiry. Recent research has indicated that ethical concerns are insufficiently dealt with in dissertations. To examine which research ethical topics were addressed and how these were presented in terms of complexity of reasoning in Swedish nurses' dissertations. Analyses of ethical content and complexity of ethical reasoning were performed on 64 Swedish nurses' PhD dissertations dated 2007. A total of seven ethical topics were identified: ethical approval (94% of the dissertations), information and informed consent (86%), confidentiality (67%), ethical aspects of methods (61%), use of ethical principles and regulations (39%), rationale for the study (20%) and fair participant selection (14%). Four of those of topics were most frequently addressed: the majority of dissertations (72%) included 3-5 issues. While many ethical concerns, by their nature, involve systematic concepts or metasystematic principles, ethical reasoning scored predominantly at lesser levels of complexity: abstract (6% of the dissertations), formal (84%) and systematic (10%). Research ethics are inadequately covered in most dissertations by nurses in Sweden. Important ethical concerns are missing, and the complexity of reasoning on ethical principles, motives and implications is insufficient. This is partly due to traditions and norms that discount ethical concerns but is probably also a reflection of the ability of PhD students and supervisors to handle complexity in general. It is suggested that the importance of ethical considerations should be emphasised in graduate and post-graduate studies and that individuals with capacity to deal with systematic and metasystematic concepts are recruited to senior research positions.