In the Improving Diagnosis in Health Care report, the National Academy of Medicine proclaimed that diagnostic errors are common, cause substantial morbidity, and are understudied. This report has led to multidisciplinary efforts to measure diagnostic error rates in both ambulatory and inpatient settings. This study examined the prevalence of three diagnostic errors in pediatric primary care practices. They found that diagnostic errors were common. Providers did not follow up abnormal laboratory values for 11% of patients and did not address adolescent depression in 62% of visits. These high rates are similar to those found in other practice settings. The authors discuss an ongoing quality improvement collaborative working to reduce diagnostic errors in pediatric primary care practices. Previous WebM&M commentaries highlight cognitive and system-level interventions to prevent diagnostic errors.