This is a Phase III, multicenter, open-label extension, single-group study in male and female outpatients with mild-to-moderate Alzheimer's disease (AD) who have completed either AVA102670 or AVA102672. All subjects will receive rosiglitazone extended-release (RSG XR) 4mg once daily for the first 4 weeks of the study followed by 8mg RSG XR as adjunctive therapy to their existing dose of acetylcholinesterase inhibitor. Subject participation will last until one of 5 conditions applies. After a 52-week open-label treatment phase, subjects will attend a final Follow-Up Visit 6 weeks after the end of treatment. The primary objective of this study is to evaluate the long-term safety and tolerability of RSG XR in subjects with mild-to-moderate AD who have completed either AVA102670 or AVA102672. The secondary objective of this study is to explore further the long-term efficacy of RSG XR in terms of cognitive function and overall clinical response as a function of apolipoprotein E (APOE) e4 allele status.