Series of N-of-1 trials have long been used to help decide the usefulness of interventions in psychology, often where conventional trial designs are impractical or unethical. Recently, N-of-1 trials have been adopted to make decisions on the usefulness of a proven therapy in individual patients. Their use is increasing because many people do not respond to a proven treatment, a greater desire to individualize therapy to enhance the risk/benefit ratio, and cost-containment pressures. N-of-1 trials reduce between-subject variability. They are useful in chronic diseases, where the effects of the active treatment are unlikely to carry-over to the next treatment period. N-of-1 trials provide a unique vehicle for the collection of economic data. Unlike most crossover trials, N-of-1 trials typically involve repeated episodes of the alternative treatments being administered over consecutive cycles. This means that each patient in a series of N-of-1 trials provides multiple observations for each treatment considered. As the required sample size for the economic components of clinical trials have been shown to be large, such trials offer an alternative to large samples that may be unfeasible. In addition, N-of-1 trials provide the means to estimate individual cost-effectiveness ratios, which may be incorporated into the patient, or clinician, decision making process. The problem of follow-up must be addressed, particularly as evaluations measuring QALYs necessarily require a life time horizon. However, if an intermediate outcome can be identified, enabling extrapolation, then this problem can be addressed. Specific examples of the use of this design will be illustrated from the field of dementia, where the 'number needed to treat' to obtain benefit in one patient is high from symptomatic improvement by approved cholinergic agents. The role of economic data from N-of-1 trials to help drug development will also be discussed.