25 years after his death, Louis Althusser's writings continue to stir up controversy.This article analyzes an issue that aroused criticism during the 1960s, an extremely polemical moment within his intellectual production: the relation between science and ideology.Is it plain opposition?Are science and ideology two clearly differentiated structures?Does science mean the end of ideology?Does science represent the truth and ideology a mere error?The article thoroughly studies Althusser's publications during the period of the 1960s in order to shed light on his thinking regarding this topic.