To gain better understanding of the natural history of Schistosoma haematobium associated disease, age- and intensity-related urinary tract morbidity were assessed in a cross-sectional study of Kilole (population 719) in Coast Province, Kenya. Overall prevalence of infection was 65% (39% light, 16% moderate, 9% heavy). Infection prevalence and mean intensity of infection were highest in the 5-14-year-old bracket for both sexes. Although significant intensity-associated increases in hematuria prevalence were noted for both children and adults in all infection categories, hematuria was more common in those less than 15 years of age. Children had a significant increase in the prevalence of dysuria at higher levels of infection, whereas adults did not. Radiographic study of a 1:9 random sample, stratified for age, revealed a greater prevalence of urinary tract granulomas in those less than 15 years. Subjects greater than 15 years of age had a greater frequency of hydronephrosis. Hydronephrosis, hydroureter, and bladder calcification were not associated with higher infection intensity. Among individuals with bladder calcification, a potential marker of cumulative inflammation, 87% had hydronephrosis or hydroureter, compared to a 40% prevalence among individuals without bladder calcification. These findings suggest that certain structural forms of urinary tract disease, such as hydronephrosis, progress during the course of untreated schistosomiasis haematobia despite age-related reductions in egg burden, whereas other forms of morbidity, such as hematuria, remain sensitive to the level of urinary egg excretion at the time of diagnosis.