Misdiagnosis of infections can lead to overuse of antibiotics and threaten patient safety. This article describes the development of two National Quality Forum (NQF)-endorsed measures of inappropriate diagnosis of urinary tract infection (UTI) and community-acquired pneumonia (CAP). Both measures demonstrated strong validity and reliability through testing with patient focus groups and case review. Implementation evaluation across more than 40 Michigan hospitals demonstrated significant decreases in inappropriate diagnoses of UTI and CAP, indicating broad usability of these measures to support improved outcomes.