OBJECTIVE: The Centers for Disease Control and Prevention's National Public Health Performance Standards Program (NPHPSP) has developed instruments to measure the performance of local and state public health departments on the 10 "Essential Services of Public Health," which have been tested in several states. This article is a report of the evaluation of the content and criterion validity of the local public health performance assessment instrument, and the content validity of the state public health performance assessment instrument. METHODS: Health department performance is measured using a set of indicators developed for the 10 Essential Services of Public Health and a model standard for each indicator. Content validity of each model standard in the local instrument was addressed by community partners along the following dimensions: the importance of each standard as a measure of the associated Essential Service, its completeness as a measure, and its reasonableness for achievement. All standards for each Essential Service were then judged in terms of their completeness in measuring performance in that service. Content validity of the state instrument was evaluated in a group interview of health department staff members from three states. Criterion validity of the local instrument was assessed for a sample of eight public health departments in Florida and six in New York by examining documentary evidence for selected responses. Criterion validity was also evaluated for a sample of Florida local public health departments and one Hawaii public health department by comparing state health department staffs' judgments of performance against the instrument score. RESULTS: Criterion validity was upheld for a summary performance score on the local instrument, but was not upheld for performance judgments on individual Essential Services. The NPHPSP standards based on the Essential Services have validity for measuring local public health system performance, according to community partners. The model standards are valid measures of state performance, according to state public health departments in three states. CONCLUSIONS: Within the scope of the validity evaluations completed, the NPHPSP state and local performance assessment instruments were found to be valid measures of public health performance.