This chapter addresses issues of data quality that affect the interpretation of reported mortality levels and trends in the New Independent States (NIS). It presents an overview of data quality issues for readers who are not necessarily specialists in demography or familiar with the quality and types of data that are available from this part of the world. We examine data from selected regions and dates, while drawing the reader's attention to broader issues and the existing literature on the quality of data from the former Soviet Union. Our focus is on the traditionally Moslem NIS countries, including the Central Asian states of Kyrgyz, Tajikistan, Turkmenistan, and Uzbekistan, plus Kazakstan and Azerbaijan, which are linked both historically and culturally to Central Asia; these are cases in which real levels and trends in mortality, both past and present, are obscured by data error. The purpose of the analysis is to identify ways of improving data collection in the NIS, especially Central Asia, so that policies and interventions related to health and mortality can be more effectively developed and targeted.