OBJECTIVES: Cholinesterase inhibitors and the NMDA-receptor modulator memantine present the first-line pharmacotherapy for Alzheimer's disease, the most common type of dementia. Effective and safe therapy requires drug administration in a particular dose regimen, at specified times, and for a specific period of time. The present study sets out to assess the adherence of ambulatory Alzheimer patients to antidementia drugs by means of electronic monitoring. METHODS: Adherence was prospectively measured using MEMS (medication event monitoring system). MEMS presents a medication container with a microprocessor in the lid that records the date and time of every opening. The study design comprises a one month run-in phase followed by a main phase lasting six months. Percentage of days with correctly administered doses of medication (daily adherence) in the main phase, and number of patients with at least one monthly (30 day period) daily adherence less than 80% were defined as main outcome measures. RESULTS: Adherence was assessed in 16 patients (11 taking a once daily medication, 5 a twice daily). Patients were prescribed one of the following drugs: donepezil (n = 7), galantamine (n = 4), memantine (n = 4), rivastigmine (n = 1). Daily adherence in main phase varied from 48.3% to 99.4% (mean = 90.5%, median = 93.6%, SD = 12.4%). A total of 5/16 patients (31%) had at least one monthly adherence less than 80%. CONCLUSION: In general, the study revealed a good medication taking behaviour with one non-adherent day out of ten on average. Nevertheless, several individuals exhibited major discrepancies that may potentially endanger therapeutic goals. In a next step, another cohort of patients and their caregivers will receive a pharmaceutical care intervention including MEMS data feedback which might help to optimize adherence.