The purpose of our research is to understand how postdoctoral researchers (postdocs) at Dutch research universities experience their working conditions, their further career prospects and opportunities, in relation to their mental health and wellbeing. The postdoc population is substantial and growing. Given that their lack of career prospects and invisibility do not coincide with their highly educated status and contribution to research, we diagnosed a dual controversy. Our recent multi-method research based on a survey amongst 676 postdocs revealed that this dual controversy results in high stress levels amongst the postdocs working at nine Dutch universities; evidence suggests that about 40% of the respondents reported serious problems concerning their mental health. Main stress factors involve lack of academic career prospects; publication and grant pressure; work--life imbalance; and the absence of institutional support. Also, several compensating factors were found, which resulted in an ambivalent or balanced situation. Encouragement from supervisors and colleagues can generally result in a better mental health.