Physical activity is an important component in the maintenance and improvement of general health; physical inactivity is, however, an increasing problem in the Netherlands. Requests for advice on physical activity are increasing within the healthcare. Assessment of an individual's physical activity pattern is required to provide tailored advice. There are a number of methods for measuring physical activity; these are divided into subjective and objective methods. Subjective measures include physical activity questionnaires and diaries. Objective measures include indirect calorimetry, measurement with doubly labelled water, heart-rate monitoring and the use of an accelerometer or pedometer. The choice of method depends predominantly on the aim of the measurement, and the availability of personnel, time and financial resources. In clinical practice a validated questionnaire is usually the preferred method, but when measuring effects this should be combined with an objective measurement instrument.