With the current decentralization of health care in the Mexican state of Guerrero, there is need for detailed but inexpensive information for the planning of health services. A cyclical process of measurement is proposed using sentinel sites, characterized as places of concentration of measurement resources, which are not special intervention areas or health facilities. The sites in Guerrero were selected to be representative of the health conditions in the state. During the first two years, study cycles were carried out regarding acute respiratory infections and diarrhoeas in infants, the risk factors associated with these afflictions and the attention paid to them within the community. Later cycles focussed on the importance of scorpion stings and Chagas' disease, the impact of measles vaccination and the prevalence of tuberculosis. Three types of community-based data are considered in each cycle, to optimize their use in planning (impact, coverage and costs) which, in summary formats, facilitate rapid analysis and presentation.