The concept of mental hygiene is historically intertwined with eugenics and what it meant both ideologically and for the care of the mentally ill. A closer investigation of the concept and of the historical context shows that different interpretations existed simultaneously. The aim of this essay is to highlight the literary and scientific works of a Swedish psychiatrist, Josef Lundahl, an advocate of the mental hygiene concept. A close reading of his texts is used to provide an example of how the concept of mental hygiene was understood by a psychiatrist and practitioner of mental hygiene. The practice of child-care and out-patient care that Lundahl founded in Visby is far from what we now associate with mental hygiene in the past.