OBJECTIVES:  Major depressive disorder (MDD) is a psychiatric condition principally characterized by depressive mood, loss of appetite, decreased interest in daily activities, sleep, behavioural or attentional disorders, diminution of energy, and feelings of guilt. Because MDD is associated with substantial health care costs and productivity losses, it wields a considerable economic impact. The aim of this study was to assess, in the Canadian context, the economic impact of escitalopram in the treatment of MDD. METHODS:  A cost-utility analysis was performed over a one-year time horizon from societal and health care system perspectives in Canada. A decision tree was developed to compare the cost per quality adjusted life year (QALY) associated with the use of escitalopram and citalopram. The decision tree, which included patients with MDD who had received escitalopram or citalopram as initial treatment, takes into account the probability of initial and subsequent treatment remission, of relapse, of suicide attempts, and of suicide-related death. Costs included were those of the antidepressant drugs, medical visits and hospitalizations, and those associated with remission/non-remission, relapses, suicide attempts and suicide-related deaths. Costs related to productivity loss and societal costs associated with suicide-related deaths were also included in the analysis with the societal perspective. Utility values associated with remission and non-remission were obtained from the literature. RESULTS:  From a health care perspective, the incremental cost-utility ratio of escitalopram compared to citalopram was estimated at $12,869/QALY. From a societal perspective, escitalopram provided more QALYs (+0.0085 QALY/patient) and entailed fewer costs (-$144.70/patient) compared to citalopram. Deterministic and probabilistic sensitivity analyses confirmed the robustness of the base-case results. CONCLUSIONS:  The results of this economic evaluation indicate that escitalopram is a more cost-effective alternative than citalopram to treat MDD from both the health care system and societal perspectives.