Environmental health problems related to water supply and sanitation conditions in urban areas of Central America are documented in this study. The task was carried out in two stages. First, a set of environmental health indicators -- in the areas of water supply, sanitation and wastewater, solid waste, hazardous waste, water pollution, food hygiene, and morbidity and mortality -- was developed. a special effort was made to collect data that distinguished formal urban areas from informal or periurban areas. Next, field trips were made to Guatemala City, Tegucigalpa, and San Salvador to collect secondary data. However, only about 25% of the data sought were actually collected, making a region wide quantitative assessment of environmental health problems impossible. There was almost a total lack of official data on informal areas, although anecdotal evidence and local studies made up for this somewhat. Conservative estimates are that: (1) 5-10% of urban populations have no sanitary facilities whatever, and 30% use latrines which, because of their concentration, may contaminate groundwater; (2) sewage is not treated, but simply moved from one area of the city to another, often to surface waters used for drinking; (3) hazardous wastes from industries and hospitals are treated the same way as other wastes; (4) wastes from hundreds of formal and probably thousands of informal industries are not regulated; (5) 50% of all solid waste is left uncollected near homes, while the other 50% is disposed in unsanitary landfills; (6) the effects of pollution on health in periurban areas seems far greater than in formal areas. Short-, medium- and long-term recommendations for USAID action to improve data availability are presented in conclusion.