OBJECTIVES:   Buprenorphine medication assisted treatment (B-MAT) is an effective therapy for opioid use disorder (OUD) but may be considered cost-prohibitive based on pharmacy cost alone.  This study estimated buprenorphine adherence and associated healthcare costs within a sample of OUD patients treated with B-MAT.  METHODS: Medical and pharmacy claims for members with a diagnosis of opioid dependence (ICD-9 304.0 and 304.7), abuse (305.5), or poisoning (965.0) were provided by Aetna (Blue Bell, PA) from Q1 2012 through Q1 2015.  B-MAT members were identified and placed into adherent (n = 205) or non-adherent (n = 272) groups based on their one-year buprenorphine medication possession ratio (MPR of ≥ 0.80).  Buprenorphine non-adherence was further examined by dividing the non-adherent group into 4 subgroups by 0.20 MPR increments.   Healthcare service utilization and expenditure was measured over the 12-month period following B-MAT initiation.  Service utilization and cost differences between groups were assessed via Mann-Whitney U tests; chi-square tests of equality of proportions were used for categorical variables.  Linear contrasts were estimated with one-way analyses of variance of logged-transformed costs.  RESULTS: Compared to non-adherent members, adherent members incurred significantly greater office visits, total prescription fills, and pharmacy costs (ps < 0.01), but significantly lower outpatient hospital, ER, and inpatient visits and costs, and overall medical costs (ps < 0.05).  The MPR subgroups demonstrated statistically significant linear contrasts on four cost metrics: pharmacy, outpatient hospital, inpatient hospital, and total medical (ps < 0.05).  With the exception of pharmacy costs, which increased with MPR, increased adherence was associated with overall decreased healthcare costs.  CONCLUSIONS: Buprenorphine adherence is associated with increased pharmacy costs, but reduced high cost venue services and overall medical costs compared to non-adherence.  The linear relationships observed in this study are evidence of a direct link between B-MAT adherence and reduced total medical expenditure.