[Page 3463]The Symptom Checklist 90 (SCL-90), developed by Leonard R. Derogatis in 1977, is one of the most widely used self-report rating scales measuring psychological distress and psychopathological symptoms in both patient and nonpatient samples. The scale is used mostly by professionals in mental health, medical, and educational settings for monitoring a patient’s progress or treatment outcome. The scale is also used for research purposes, including researching topics such as public health, psychological well-being, and trauma. After briefly describing the development of the SCL-90, this entry discusses the SCL-90’s characteristics, administration, and psychometric properties.