To evaluate the efficacy and safety of bimatoprost plus timolol fixed combination (BTFC) in patients with primary open angle glaucoma (POAG) previously treated with dorzolamide plus timolol fixed combination (DTFC). Retrospective, medical records review study. Medical records of patients with POAG previously treated with DTFC and then switched to BTFC for poor intraocular pressure (IOP) control or ocular discomfort were included in the analysis. One baseline IOP diurnal curve, and one diurnal curve under each treatment were required to be eligible for this study. The primary outcome was to compare the mean diurnal IOP between DTFC and BTFC. Secondary outcomes were to compare the IOP diurnal fluctuation, and the percentage of patients achieving a target IOP <14, <16, and <18 mmHg between the two treatments. Medical records of 96 patients were analyzed (mean age 65.8 years ± 7.2, range 39-89 years). The mean diurnal IOP was 23.7 ± 3.8 mmHg at baseline, 16.9 ± 3.4 mmHg with DTFC and 15.1 ± 2.9 mmHg after therapy was switched to BTFC (p < 0.0001 each treatment vs baseline; p < 0.0001 DTFC vs BTFC). The proportion of patients achieving a mean diurnal IOP <18, <16, and <14 mmHg was 76%, 35.4%, and 12.5% with DTFC and 81.2%, 68.8%, and 37.5% with BTFC (p = 0.20, p < 0.01, and p < 0.0001 between the two treatments, respectively). IOP fluctuation did not differ significantly between the treatments. BTFC can provide additional lowering in the mean diurnal IOP in patients previously treated with DTFC with no significant differences in the safety and tolerability profile.