The purpose of this study is to evaluate the long-term safety and tolerability of ABT-089 in adults with mild-to-moderate Alzheimer's disease.

Inclusion Criteria:

• The subject was randomized into Study M06-876 and completed the study.
• The subject must remain on the same dose of AChEI that was used during the M06-876 study.
• The subject is in general good health, as judged by the investigator

Exclusion Criteria:

• The subject is currently, or plans to participate in another experimental study during the course of this trial.
• The subject anticipates a move outside the geographic area of the investigative site or is planning extended travel inconsistent with the recommended visit intervals.