Diarrhea is a leading cause of sickness and death of beef and dairy calves in their first month of life. Field investigations of outbreaks of neonatal calf diarrhea should be conducted for the purposes of (1) reducing the losses associated with existing cases and (2) preventing new cases from occurring. The appropriate corrective actions are determined by taking a population approach to diagnostics and prevention. It can be difficult to provide solutions to disease outbreaks, but success is more likely if an organized, epidemiologic approach to outbreak investigation is followed.