With the improved control of acute diarrheal illness mortality with oral rehydration therapy, persistent diarrhea is now emerging as a major cause of childhood mortality in tropical developing areas like the impoverished populations in Brazil's Northeast. "Graveyard surveillance" in the rural community of Guaiuba in northeastern Brazil revealed fully half of the 70% diarrhea mortality was due to persistent diarrheal illnesses. Furthermore, 11% of 14 or more diarrheal illnesses per child per year in an urban slum in Fortaleza persisted beyond 14 days, a definition that clearly identified the high risk children for heavy diarrhea burdens. Not only did heavy diarrhea burdens ablate the key "catch-up" growth seen in severely malnourished children and in children following previous diarrheal illnesses, but malnutrition significantly predisposed children to a greater incidence and duration of diarrhea as well as a greater incidence of persistent diarrhea. Etiologic studies of 37 children presenting with persistent diarrhea to Hospital das Clinicas in Fortaleza revealed that Cryptosporidium (in 13%) and enteroadherent E. coli (36% with aggregative, 29% with diffuse and 13% with localized adherence to HEp-2 cells) were the predominant potential pathogens found in the stool or upper small bowel. These findings suggest that persistent diarrhea is emerging as an important health problem in Brazil's Northeast, that it identifies a high risk child for heavy diarrhea burdens, that important interactions occur with malnutrition and that Cryptosporidium and enteroadherent E. coli warrant further study as potential etiologies of this major cause of morbidity and mortality.