The Mobile Emergency Medical Service (SAMU) was the first component of the National Policy for Emergency Care implemented in Brazil in the early 2000. The article analyzed the implementation of mobile pre-hospital emergency care in Brazil. The methods included document analysis, interviews with state emergency care coordinators, and an expert panel. The theoretical reference was the strategic conduct analysis from Giddens' Structuration Theory. The results showed uneven implementation of the SAMU between states and regions of Brazil, identifying six patterns of implementation, considering the states' capacity to expand the population coverage and regionalize the service. Structural difficulties included physician retention, poorly equipped dispatch centers, and shortage of ambulances. The North and Northeast were the country's most heavily affected regions. SAMU is formatted as a structuring strategy in the emergency care network, but its performance suffered the impact of limited participation by primary care in the emergency network and especially the lack of hospital beds.