Stool cultures can be important in guiding antimicrobial therapy for diarrhea. From among 11.64 million person-years of Tennessee Medicaid enrollment data collected from 1995 through 2004, 315,828 diarrheal episodes were identified. Stool cultures were performed for only 15,820 episodes (5.0%). Antimicrobials were prescribed for 32,949 episodes (10.4%), 89.4% of which were not accompanied by a stool culture. White race and urban residence were associated with higher rates of stool culture. Frequent use of antimicrobials for diarrhea without stool culture may indicate inappropriate antimicrobial use and has critical implications for public health.