Objective: To use clinical and functional characteristics observed upon admission to an emergency room to identify factors predictive of the occurrence and course of acute asthma attacks in children. Methods: We prospectively studied 130 asthmatic children, from 1 to 13 years of age, who were treated for acute asthma attacks in an emergency room, evaluating status determined at admission and over the course of the crisis. Clinical scores were determined and arterial oxygen saturation by pulse oximetry was measured, as was peak expiratory flow. Results: The initial clinical score, arterial oxygen saturation by pulse oximetry and peak expiratory flow correlated with the number of inhalations performed, as well as with the need for corticosteroid treatment. Mean initial clinical score and mean arterial oxygen saturation by pulse oximetry of the hospitalized patients were statistically different from those of patients who were not hospitalized. Initial clinical score, arterial oxygen saturation and prior treatment for the same exacerbation were predictive of the need for hospitalization. Conclusion: The measurement of arterial oxygen saturation by pulse oximetry and the clinical score were useful in predicting the occurrence and course of acute asthma attacks in children. The measurement and interpretation of peak expiratory flow is difficult in children and, under these conditions, served no practical application.