To assess understanding of numerical concepts in asthma self-management instructions, a 4-item Asthma Numeracy Questionnaire (ANQ) was developed and read to 73 adults with persistent asthma. Participants completed the Short Test of Functional Health Literacy in Adults (STOFHLA), 12(16%) answered all 4 numeracy items correctly; 6(8%) answered none correctly. Participants were least likely to understand items involving risk and percentages. Low numeracy but not STOFHLA score was associated with a history of hospitalization for asthma. At higher STOFHLA levels there was a wide range of the total number of correct numeracy responses. Numeracy is a unique and important component of health literacy.