Once-daily topical brimonidine tartrate (BT) gel 0.5% was shown to be efficacious and safe for the treatment of erythema of rosacea in previous studies including a 4-week treatment phase. In the present 1-year study, we aimed to assess the long-term safety and efficacy of the treatment. Subjects with moderate to severe erythema of rosacea were instructed to apply topical BT gel 0.5% once daily for 12 months. Severity of erythema and adverse events (AEs) were evaluated. Approximately 345 subject years of exposure to BT gel 0.5% was achieved in the study. The incidence of AEs and AEs judged to be related to the study drug was higher at the beginning and decreased over the course of the study. Similar safety profiles were observed between the subjects who had received or not received concomitant therapies for the inflammatory lesions of rosacea. Effect of topical BT gel 0.5% on erythema severity was observed after the first application and the durability of the effect was maintained until the end of the study at month 12, with no tachyphylaxis observed. In conclusion, once-daily topical BT gel 0.5% is safe and consistently effective for the long-term treatment of moderate to severe erythema of rosacea, even in the presence of concomitant therapies for the inflammatory lesions of rosacea.