This article examines the impact of exposure to ideological online news media on political misperceptions. Using data from a representative survey conducted during the 2012 U.S. presidential election, the study tests three theoretical mechanisms by which biased news sites might influence beliefs: reducing awareness of relevant evidence, misrepresenting that evidence, and encouraging users to adopt outlet-favored views regardless of the evidence. The findings suggest that ideological media exposure consistently promotes misperceptions, regardless of whether individuals are aware of the evidence. Specifically, conservative news use is associated with greater accuracy about liberal-favored misperceptions and less accuracy about conservative-favored misperceptions, while liberal news use has the opposite effect. The study also finds no evidence that ideological media reduce awareness of politically unfavorable evidence, though they do promote misunderstandings of it in some cases. These results highlight the importance of biased news in shaping political beliefs and suggest that efforts to reduce misperceptions may need to address the influence of ideological media on beliefs rather than just knowledge.This article examines the impact of exposure to ideological online news media on political misperceptions. Using data from a representative survey conducted during the 2012 U.S. presidential election, the study tests three theoretical mechanisms by which biased news sites might influence beliefs: reducing awareness of relevant evidence, misrepresenting that evidence, and encouraging users to adopt outlet-favored views regardless of the evidence. The findings suggest that ideological media exposure consistently promotes misperceptions, regardless of whether individuals are aware of the evidence. Specifically, conservative news use is associated with greater accuracy about liberal-favored misperceptions and less accuracy about conservative-favored misperceptions, while liberal news use has the opposite effect. The study also finds no evidence that ideological media reduce awareness of politically unfavorable evidence, though they do promote misunderstandings of it in some cases. These results highlight the importance of biased news in shaping political beliefs and suggest that efforts to reduce misperceptions may need to address the influence of ideological media on beliefs rather than just knowledge.