The Association of Socialist Physicians (ASP) was the most important left-wing medical association during the Weimar Republic. Its primary goal was the introduction of a free healthcare system, in line with the principles described in the SPD’s Erfurt Program of 1891. Max Hodann, whose areas of research focused on social hygiene, sexual reforms and eugenics, was one of the most well-known members of the ASP and was strongly involved in the German youth movement. This article traces Hodann’s scientific and political development, especially with regard to the critique of the SPD’s policy. Furthermore, the extent to which this development was related to his ideas on health policy and social hygiene, issues for which Hodann was regarded as the most outspoken representative within the ASP, is being discussed.