Acute diarrheal illness (illness of less than two weeks' duration) accounts for numerous out-patient health care visits. This article provides an overview of the most common causes of acute diarrhea and presents a comprehensive approach to patient evaluation, diagnosis and management. A detailed outline of bacterial, viral, parasitic and travelers' diarrheal disorders is presented. Dysentery (blood and mucus in the stool) represents an additional challenge to the health care provider. Salient historical data, physical assessment and laboratory considerations are reviewed. Management objectives including diet/fluid replacement, pharmacologic modalities and prophylaxis are described. Emphasis is given to patient education and the unique role of the nurse practitioner in assisting the patient through the assessment and management of this common, distressing problem.