It has been demonstrated in previous studies that Providencia alcalifaciens can produce diarrhea by an invasive mechanism. In the present study, P. alcalifaciens was isolated from the stool specimens of 17 of 814 diarrheal children younger than 5 years of age (2.1%) and from those of 4 of 814 matched controls (0.49%) (P = 0.004), indicating that the organism is significantly associated with diarrhea. However, 71% of P. alcalifaciens-positive diarrheal children had simultaneous infections with other recognized enteric pathogens.