BACKGROUND: Depressive and anxiety disorders commonly occur together in patients presenting in the primary care setting. Although recognition of individual depressive and anxiety disorders has increased substantially in the past decade, recognition of comorbidity still lags. The current report reviews the epidemiology, clinical implications, and management of comorbidity in the primary care setting. METHOD: Literature was reviewed by 2 methods: (1) a MEDLINE search (1980-2001) using the key words depression, depressivedisorders, and anxietydisorders; comorbidity was also searched with individual anxiety diagnoses; and (2) direct search of psychiatry, primary care, and internal medicine journals over the past 5 years. RESULTS: Between 10% and 20% of adults in any given 12-month period will visit their primary care physician during an anxiety or depressive disorder episode (although typically for a nonpsychiatric complaint); more than 50% of these patients suffer from a comorbid second depressive or anxiety disorder. The presence of depressive/anxiety comorbidity substantially increases medical utilization and is associated with greater chronicity, slower recovery, increased rates of recurrence, and greater psychosocial disability. Typically, long-term treatment is indicated, although far less research is available to guide treatment decisions. Selective serotonin reuptake inhibitor antidepressants are the preferred treatment based on efficacy, safety, and tolerability criteria. Knowledge of their differential clinical and pharmacokinetic profiles can assist in optimizing treatment. CONCLUSION: Increased recognition of the high prevalence and negative psychosocial impact of depression and anxiety disorder comorbidity will lead to more effective treatment. While it is hoped that early and effective intervention will yield long-term benefits, research is needed to confirm this.