Malaria is a public health problem in Peten, Guatemala. Due to strategic changes of malaria control programs (MCPs), more efficient tools for assessing their effectiveness are required. A GIS was developed and used locally to analyze the malaria situation, to evaluate the surveillance system performance, and to orient the necessary adjustments for control. Information on malaria cases in 1993 was selected from the MCP database and linked with other databases. Rivers and roads were used to help define village accessibility. Malaria incidence levels by village showed a wide range including villages where no cases were reported. Other indicators of diagnostic coverage were further used to evaluate those areas of "epidemiological silence." There was a tendency of malaria to cluster in certain low altitude areas (a proxy for anopheline species distribution), in particular where more recent deforestation had taken place. The occurrence of severe (falciparum) malaria did not show a definite pattern. The spatial distribution of health services was also analyzed to define their catchment areas. There was an overlap of health services along more accessible areas while leaving others with little or no coverage, in particular where malaria incidence was higher with lower accessibility (as defined by access by boat). This information indicated the need to redistribute resources to areas with higher incidence and no coverage and/or use alternative strategies to cover areas with difficult accessibility. Other GIS tools (spatial aggregate, proximity) were used to define the population in the catchment areas and distance calculation for village visits and thus helped to plan and program the resources needed. GISs are relatively simple tools that allowed the overlay of different spatially related information for the characterization of malaria problem areas and can be used at the local level for MCP evaluation and planning.