The authors present a method for modeling cost data on three selective serotonin reuptake inhibitors (SSRIs)-fluoxetine, paroxetine, and sertraline-from a large clinical outcomes study in a university-affiliated mental health center. Using data from 2,779 patients, average drug cost per day was calculated based on the percentage of patients on each daily dose of each medication. Given no overall significant difference between the SSRIs in effectiveness, the actual average cost per day determined by dose distribution was $1.79 for fluoxetine, $1.41 for paroxetine, and $1.21 for sertraline (using halved 100 mg tablets). The results suggest that cost can serve as one measure to help guide choice of medications.