A method and system for classifying messages of a discussion thread as questions is provided. A classification system generates a classifier to classify messages of discussion threads as question messages or non-question messages. The system trains the classifier using the feature vectors and input classifications derived from a training set of discussion threads. After the classifier is trained, the classification system uses the classifier to classify messages within a corpus of discussion threads as question or non-question messages. To classify a message, the classification system generates a feature vector for the messages and submits that feature vector to the classifier. The classifier generates a score for the message indicating a likelihood that the message is a question message.