Auditing a clinical trial is a complex process designed to ensure that the trial will provide a reliable answer to the question being posed. Traditional auditing methods are expensive, and escalate the cost of clinical trials. This paper describes approaches to cost-effective monitoring of clinical trials, such as integrating them with clinical practice and focusing the data being collected. Sampling methods for source documentation can be used to eliminate costs incurred by reviewing every record. These measures, coupled with prospective clinical judgment about areas of concern in the conduct of trials, can reduce complications and costs without sacrificing quality.