Numeracy, the "ability to understand and use numbers in daily life" is an important but understudied component of literacy. Numeracy-related tasks are common in health care and include understanding nutrition information, interpreting blood sugar readings and other clinical data, adjusting medications, and understanding probability in risk communication. While literacy and numeracy are strongly correlated, we have identified many patients with adequate reading ability but poor numeracy skills. Better tools to measure numeracy and more studies to assess the unique contribution of numeracy are needed. This research can contribute to developing interventions to improve outcomes for patients with poor numeracy.