The study objective was to determine the impact on quality of care, resource use, and outcomes by developing an emergency department (ED)-based asthma-specific care plan. The design was a time based, prospective cohort and set at an urban university/trauma center, EM residency site, combined adult/pediatric department. Best practice was defined prospectively for ED asthma patients, leading to an asthma care plan (ACP). Triage nurses were instructed to begin use of ACP when patients presented with asthma as the primary complaint. Charts of all patients diagnosed with asthma during 3-month study period were retrospectively reviewed against predefined outcomes. Results were analyzed with χ² or student's t tests. After ACP introduction, the timeliness of β agonist treatments (three β agonist treatments within 90 minutes; 86% versus 63%, P < .05) and ED length of stay (LOS) (3.39 ± 1.88 hrs versus 3.87 ± 2.12 hrs, P < .05) improved. After introduction of ACP, only 55% of patients diagnosed with asthma had care documented on the ACP (ACP + group). ACP + group had more timely β agonist treatment (93% versus 74%, P < .01), shorter LOS (3.29 ± 1.90 vs. 3.53 ± 1.86 hrs, P < 0.5) more appropriate steroid dosages (67% versus 41%, P < .01), and fewer tests (41% versus 59%, P < .05). No improvements were noted in admission or relapse rates. In conclusion, care plans can improve quality of care and decrease LOS, but may have limited impact on outcomes of admission/discharge or relapse rates. (Am J Emerg Med 2000;18:367-371. Copyright © 2000 by W.B. Saunders Company)