OBJECTIVES: To determine whether sub-acute lack of asthma control (SALAC), independent of current exacerbations, is associated with subsequent acute asthma exacerbations. METHODS: Patients who were aged ³12 years as of 2001, continuously enrolled throughout 2001-2004, and had ³1 claims for asthma (ICD-9-CM code 493.x), no claims for COPD or cystic fibrosis, and ³1 prescriptions for an asthma medication anytime during 2001-2004 were identified using administrative claims data from PharMetrics/IMS Health. SALAC was defined as >4 physician visits for asthma per year (or ³2 per quarter) or >5 SABA prescriptions per year. The impact of asthma control category during 2001 (exacerbation only, SALAC only, both exacerbation and SALAC, or neither exacerbation nor SALAC) on having ³1 acute asthma exacerbations (hospital admissions, ED visits, or short-term courses of oral corticosteroid therapy within 7 days of a physician office visit) anytime during 2002-2004 was assessed using logistic regression. Covariates included gender, age, insurance type, and region. RESULTS: Among 11,779 asthma patients in 2001, 8% experienced an exacerbation only (EO), 26% experienced SALAC only (SO), 12% had both an exacerbation and SALAC (Both), and 54% had neither an exacerbation nor SALAC (Neither). The 2002-2004 exacerbation rate was higher in the Both group vs. the EO group (61.8% vs. 55.0%) and in the SO group vs. the Neither group (37.3% vs. 31.9%). Controlling for the covariates and compared with the Neither group, the Both group had a larger impact on the odds of an exacerbation in 2002-2004 than did the EO group (3.394 [95% CI: 3.009, 3.827] vs. 2.503 [2.176, 2.879], and the SO group had a significant and positive effect (1.277 [1.166, 1.399]). CONCLUSION: SALAC identifies an additional 26% of asthma patients who have a higher likelihood of a subsequent exacerbation in addition to the 20% who experienced an exacerbation in 2001.