OBJECTIVE: To determine the cost-effectiveness of escitalopram in the treatment of Generalized Anxiety Disorder (GAD) in Canada. GAD places a significant burden on primary care resources, exhibiting an 8% prevalence rate among patients seen by primary care clinicians. METHODS: A 24-week decision tree analytic model was constructed using Tree Age Data® Pro Suite. Patients received treatment for GAD with either escitalopram or generic paroxetine. Clinical rates were determined from a review of the literature; expert opinion guided model development in establishing decision pathways. Tolerance/intolerance to the initial drug was incorporated into the model, which included augmenting, titrating or switching comparators. Psychotherapy was used for patients not responding to either drug, or to the combination of either drug augmented with a benzodiazepine. Costs were measured in undiscounted 2005 Canadian dollars (CAD). Resources were valued using standard Canadian sources. Effectiveness was measured in Symptom Free Days (SFDs). Analyses were performed from two perspectives: the Ontario Ministry of Health and Long Term Care (MoH - included all direct costs: drugs, physicians visits), and societal (SOC-included direct plus indirect costs weighted using the average industrial wage). Extensive sensitivity analyses (1-way and probabilistic) were conducted. RESULTS: Results shown are preliminary. Base case analyses (MoH perspective) yielded an incremental cost of $24 for escitalopram (expected cost=$713 for 85 SFDs) over paroxetine (expected cost=$688 for 76 SFDs), for an incremental cost effectiveness ratio of $2.79/SFD ($1004/Symptom-free year). Paroxetine was dominated under the SOC perspective. Total expected cost from the SOC perspective was $3676 and $3529 for paroxetine and escitalopram, respectively. Sensitivity analysis was conducted on upper and lower efficacy boundaries, yielding similar incremental cost-effectiveness results. CONCLUSION: Escitalopram is cost-saving in the treatment of GAD under the SOC perspective in Canada, and appears to be cost-effective under the MoH perspective.