As the interest in Alzheimer's disease (AD) and its treatment has grown, so has the sophistication of clinical trials of potential drug therapies. In particular, interest has focused on outcomes used to assess the severity of the illness and the effectiveness of treatment. This paper reviews the assessments that are used frequently in trials of AD therapy and describes further measures that may be of value in determining effective treatments for the disease. The review concludes that it is important that evaluation of drug effects on AD is not confined solely to the assessment of cognitive function. To gain a true overview of the impact of AD on patients, carers and society, areas such as activities of daily living, caregiver burden, quality of life, behavioural symptoms and resource utilization need to be comprehensively determined.