OBJECTIVES: To describe treatment discontinuation among postmenopausal women initiating denosumab or monthly oBPs in routine clinical practice in Bulgaria. METHODS: This retrospective chart review, conducted in 12 Bulgarian endocrinology or rheumatology practices, included postmenopausal women ≥50 years old initiating denosumab or monthly oBPs between 1-Oct-2011 and 30-Sep-2012, followed up to 24 months after treatment initiation. For both denosumab and monthly oBPs, discontinuation date was taken from the patients’ medical records (including any switch to another treatment/dosing regimen). If no such date was recorded, patients’ were assumed to have continued on treatment. Denosumab persistence at 12, 18 and 24 months was defined as receiving the subsequent injection 6 months +60-days after the previous injection. Persistence to monthly oBPs could not be calculated. RESULTS: A total of 224 women initiating denosumab and 217 initiating monthly oBPs met the inclusion criteria. Of these, 57 (25%) initiating denosumab and 38 (18%) initiating monthly oBPs had experienced ≥1 prior  OP fracture; 3 (1.3%) initiating denosumab and 8 (3.7%) initiating monthly oBPs experienced ≥1 OP fracture during the follow-up period. At treatment initiation, mean (SD) BMD T-scores for the denosumab and oBPs groups were -3.2 (±0.65) and -3.0 (±0.57) at the lumbar spine, -3.2 (±0.69) and -2.8 (±0.73) at the total hip and -2.6 (±0.71) and -2.4 (±0.77) at the femoral neck. Within the 24-month follow-up, 4.5% of women initiating denosumab and 56.2% initiating monthly oBPs discontinued treatment; median (interquartile range) time to discontinuation, 729.0 (728.3„Ÿ729.0)  and 367.0 (354.0„Ÿ484.8) days, respectively. Denosumab persistence was 100%, 99.1% and 98.7% at 12, 18 and 24 months, respectively. CONCLUSIONS:   In this study of routine clinical practice in Bulgaria, only 4.5% of women initiating denosumab discontinued treatment within 24 months, compared with more than half of those initiating monthly oBPs.