Intestinal parasites appear to be prevalent in Nicaragua, which motivated a more extensive prevalence study in which socioeconomic conditions such as degree of crowding, quality of water supply, type of floor and disposal of excretion, were considered. The study was performed on 1267 stool samples from about 8% of the citizens of the city of León. The overall prevalence of intestinal pathogenic parasites among the 1267 individuals was found to be 47.2%. The prevalence of Entamoeba histolytica/dispar was 18.6% followed by Giardia (15.9%) and Ascaris (13.4%). Other helminths such as hookworms and Strongyloides sp. were found at very low rates. Giardia, in contrast to worm infections, was prevalent already in children under 5 years of age. E. histolytica/dispar increased with age and remained high. Of 595 individuals with intestinal parasites 81% were living in 'poor' conditions and in 13 clusters of households, a lower prevalence of parasites was seen in households characterised as having good socioeconomic conditions. However, several variables appear to be important in determining the prevalence of the individual intestinal protozoa and helminths encountered.