Objective: To establish the correlation among clinic classification of asthma crises, and the variables, peak expiratory flow, paradoxical pulse and oxihemoglobin saturation, to define which of these variables is more reliable like measurement of the severity of the crisis. Materials and methods: This is an evaluative descriptive study, analyzed a total of 395 events in patients between the 14 and 86 years old, during July 2005 to December 2006 in the emergency room of Hospital Universidad del Norte, obtaining data about clinical data and epidemiologists. Results: The 26,8% it happened in men and the 73,2% in women. The crises were classified like light in the 46,68%, Moderate ones in 44,38%, severe 7,90% and like imminent respiratory unemployment in 1.02%. Conclusion: This study shows to divergences between the clinical picture and the graduation of severity established by the peak expiratory flow, being observed that this measurement tends to overestimate the severity of the crisis. The oxihemoglobin saturation can identify the severe crises, but it does not establish significant differences between the light and moderate crises. The paradoxical pulse turned out to be the objective variable that was reconciled more