This two-phase, multicenter study was undertaken to examine the safety and efficacy of combination therapy with oral doxycycline and topical azelaic acid (AzA) 15% gel in moderate-to-severe papulopustular rosacea and to determine the effect of subsequent maintenance monotherapy with AzA 15% gel alone. In the initial open-label, non-randomized phase of the study, subjects (n=172) received topical AzA 15% gel and oral doxycycline (100 mg), both twice daily, for < or = 12 weeks. In the second, double-blind study phase, subjects who had initially undergone at least four weeks of combination treatment in phase 1 and who achieved > or = 75% inflammatory lesion count reduction (n=136) were randomized to receive either AzA 15% gel or its vehicle twice daily for an additional 24 weeks. Assessments of efficacy were obtained at four-week intervals throughout both phases of the study and included change in inflammatory lesion count, investigator global assessment (IGA) of rosacea severity, and separate assessments of erythema and telangiectasia severity. At the last visit for each phase of the study, the investigator and participant each rated overall improvement, with the participant rating cosmetic acceptability and the investigator rating treatment as "success" or "failure" based on IGA score. During the second phase of the trial, the rate of relapse -- defined as either a 50% deterioration in the lesion count improvement from phase 1, an increase in erythema intolerable to the subject or maintenance therapy failure as judged by the investigator and/or the subject -- was obtained. Safety assessments were conducted for both phases of the study and included analysis of adverse events (AEs) and a rating of cutaneous tolerability by the subject. By week 12 of the open-label phase of the study, 81.4% of subjects had reached a 75% or greater reduction in inflammatory lesion count, and 64% of patients achieved treatment success. During the second study phase (maintenance phase), AzA 15% gel consistently provided a better maintenance response than vehicle, with maintenance of remission in 75% of patients over the six-month duration of the maintenance phase. Additionally AzA 15% gel showed a statistically significantly lower deterioration in absolute inflammatory lesion counts than did vehicle after 8, 16, 20 and 24 weeks of maintenance therapy. No serious treatment-related AEs were encountered in the study, and 98.5% of subjects were satisfied with the local tolerability of both AzA gel and vehicle.