The Mobile Emergency Care Services handle urgent situations of various types, and demand for this service occurs according to the perception of the user regarding what is urgent. The aim of the study was to analyze the perceptions of urgency by users who demand care from a Mobile Emergency Care Service in Porto Alegre and to identify the reasons for these requests. In this explomratory-descriptive study, with qualitative approach, data were collected through semi-structured interviews conducted by telephone, during theperiod from February to April 2009. Thematic analysis was used to analyze the information. Users consider urgent life-threatening conditions, which require a quick response, and visible situations, such as bleeding, chronic diseases, and difficulties in transportation. Users themselves feel motivated to call the service due to it being rapid and free, and for transportation. The perceptions of users regarding urgency were diverse, sometimes consistent with the biomedical perspective of health providers and sometimes with their own social context.