There is a long-standing belief that elderly patients take longer to respond to antidepressant treatment than younger patients, and thus, require longer trials to respond or remit. This has led to the question: What is the minimum duration of antidepressant treatment necessary to identify responders in older depressed adults? A 12-week duration was tested based on 2 separate ideas: (1) older patients take longer to respond and, therefore, require longer trials to achieve optimal response (ie, remission), and (2) patients who are still quite symptomatic at Week 11 may improve dramatically and meet response, or even remission, criteria by Week 12. The data that support these beliefs are sparse and what little exist are contradictory. Rates of response and time-to-response were analyzed in depressed older adults in two 12-week clinical trials. The results do not support the belief that older patients take longer to respond or that, generally, as a group, older patients have a lower response rate. Furthermore, if patients do not have > or =30% reduction in baseline Hamilton Rating Score for Depression (HRSD) by Week 4, the probability that they will meet remission criteria (defined as HRSD < or =10 and HRSD < or =6) at the end of the trial is only 35% and 16.5%, respectively. Therefore, a 12-week trial is not necessary for all older patients; rather, the degree of improvement in the first 4 to 6 weeks identifies patients who are highly likely to benefit from continuing antidepressant treatment as well as those who very probably should have their treatment regimen altered at that point.