The primary outcome of interest will be a comparison of the percentage of patients who have a recurrence of major depression while continued on citalopram compared with those who were switched to placebo after the acute phase. Recurrence will be defined as meeting Diagnostic and Statistical Manual of Mental Disorders, 4th Edition (DSM-IV) criteria for major depression and a Hamilton Depression Scale (HAM-D) score of > 16. Or meeting DSM-IV criteria for major depression and having a Clinical Global Impression (CGI) severity score of >= 4 and a CGI illness score of >= 3. The HAM-D and CGI will be administered every four weeks for forty weeks.