Recent studies have identified robust associations between the types of words that people use and their psychological health. This study investigated whether couples' word use in their daily instant messages (IMs) is linked to the quality and stability of their relationships. Sixty-eight dating couples in the United States submitted 10 days of IM conversations with each other, which were analyzed with a linguistic word count program. Six months later, couples indicated whether they were still dating. Pronoun use and emotion word use both were associated with relationship satisfaction and stability. These findings extend previous research showing that the frequencies of certain words that people use are associated with the quality of their social relationships.