Approximately 10-20% of individuals with Major Depressive Disorder (MDD) fail to respond to antidepressant monotherapy.  These individuals with treatment resistant depression (TRD) have been found to be frequent users of healthcare services, thus incurring significantly greater costs than those without TRD. OBJECTIVES:  To investigate the cost of Treatment-Resistant Depression from a private payer perspective in Canada. METHODS:  An employer-sponsored benefits plan database (2011/2012) was used to define a cohort of Non-TRD and TRD claimants. TRD claimants are defined as those on their third antidepressant monotherapy; or combination antidepressant therapy; or antidepressant augmented with lithium, thyroid hormone or an antipsychotic medication.  The cost of prescription medication utilization, short-term disability (STD), and long-term disability (LTD) benefits for employees was calculated (2011 and 2012 $CAN) for both Non-TRD and TRD groups.  Descriptive statistics were used to characterize the cohort of claimants and employees, as well as resources and costs for employees. RESULTS:  There were 55,324 and 61,028 employee claimants in 2011 and 2012, respectively.  717(1.3%) and 798(1.3%) were TRD claimants; 4,744(8.6%) and 5,137(8.4%) were Non-TRD claimants in 2011 and 2012, respectively.  In 2011, the medication costs for treating depression was $774 per TRD employee claimant compared to $303 per Non-TRD claimant.  STD costs were $6,263 for TRD (n=79) and $5,855 for Non-TRD (n=276).  LTD costs were $13,598 for TRD (n=80) and $12,272 for Non-TRD (n=119).  In 2012, the medication costs for treating depression per TRD employee claimant was $794 compared to $293 for Non-TRD claimants.  STD costs were $7,832 for TRD (n=86) and $4,001 for Non-TRD (n=248).  LTD costs were $13,927 for TRD (n=89) and $12,901 for Non-TRD (n=121).  CONCLUSIONS:  Claimants identified with TRD had higher medication, STD and LTD costs than those with Non-TRD.  Limitations include lack of diagnostic information for claimants and small sample sizes for STD and LTD subgroups.