Most extractive summarization methods focus on the main body of the document from which sentences need to be extracted. The gist of the document often lies in the side information of the document, such as title and image captions. These types of side information are often available for newswire articles. We propose to explore side information in the context of single-document extractive summarization. We develop a framework for single-document summarization composed of a hierarchical document encoder and an attention-based extractor with attention over side information. We evaluate our models on a large scale news dataset. We show that extractive summarization with side information consistently outperforms its counterpart (that does not use any side information), in terms on both informativeness and fluency.