In studies with predominately male patients, B-type natriuretic peptide (BNP) levels have been shown to be helpful in the evaluation and management of patients who present with acute dyspnea. The effect of BNP levels on the management of women has not been defined. This study evaluated a predefined subgroup of 190 women included in a prospective randomized controlled study of BNP testing for emergency diagnosis of acute dyspnea. Patients were randomly assigned to a diagnostic strategy with (n = 93, BNP group) or without (n = 97, control group) the use of BNP levels provided by a rapid bedside assay. Women differed significantly from men in baseline characteristics, symptoms, signs, and final discharge diagnoses. The use of BNP levels decreased the need for hospital admission (73% vs 86%, p = 0.034) and intensive care (12% vs 23%, p = 0.048). Median time to discharge was 6 days in the BNP group versus 10 days in the control group (p = 0.023). Total cost of treatment was $4,781 in the BNP group (95% confidence interval 3,854 to 5,708) versus $6,843 in the control group (95% confidence interval 5,611 to 8,074, p = 0.009). In-hospital mortality rates were 4% in the BNP group and 10% in the control group (p = 0.165). Thus, used in conjunction with other clinical information, rapid measurement of BNP decreased time to discharge and total cost of treatment in women who presented with acute dyspnea.