The National Comorbidity Survey Replication (NCS-R) is a new nationally representative community household survey of the prevalence and correlates of mental disorders in the US. The NCS-R was carried out a decade after the original NCS. The NCS-R repeats many of the questions from the NCS and also expands the NCS questioning to include assessments based on the more recent Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) diagnostics system (American Psychiatric Association, 1994). The NCS-R was designed to (1) investigate time trends and their correlates over the decade of the 1990s and (2) expand the assessment of the prevalence and correlates of mental disorders beyond the assessment in the baseline NCS in order to address a number of important substantive and methodological issues that were raised by the NCS. This paper presents a brief review of these aims. Copyright © 2004 Whurr Publishers Ltd.