This paper focuses on the relations between a liberal group of sex reformers, consisting of writers and literary critics, and physicians from the Polish Eugenics Society in interwar Poland. It illustrates the paradoxes of the mutual co-operation between these two groups during the 1930s and analyses the reason why compulsory sterilisation was rejected by politicians. From the early 1930s two movements began to forge an alliance in Poland: the sexual reform movement which advocated freedom of the individual, and eugenics, which (...) called for limiting the freedom of the individual for the collective good. This paper draws attention to several issues which emerged as part of this collaboration: population politics, the relationship between reformers, eugenicists and state institutions, and the question of how both movements—eugenics and sexual reform—perceived the question of sexuality, birth control and abortion. It will also focus on those aspects of their thinking that led to mutual co-operation. (shrink)