We experimentally investigate information aggregation through majority voting when voters are biased. In such situations, majority voting can have a “dark side,” that is, result in groups making choices inferior to those made by individuals acting alone. In line with theoretical predictions, information on the popularity of policy choices is beneficial when a minority of voters is biased, but harmful when a majority is biased. In theory, information on the success of policy choices elsewhere de-biases voters and alleviates the inefficiency. However, in the experiment, providing social information on success is ineffective and does not sufficiently de-bias voters.