Physical activity (PA) improves exercise capacity, slower decline in lung function and improve quality of life in patients with cystic fibrosis (CF). Despite the importance of PA, it is important to assess the amount of PA. The objective of this literature review was to evaluate the validity and usability of instruments that are used to measure PA in patients with CF. GoogleScholar, ScienceDirect, The Cochrane Library and PUBMED database were searched. All studies that included instruments to measure PA of patients with CF, published from 2000 till June 2012 were reviewed. Eight studies were included in this systematic review. At this moment, there is not sufficient evidence to support incorporation of specific tools to facilitate the PA assessment into clinical practice. Pedometers may offer an inexpensive method of obtaining a measurement of PA, and there is some evidence for supporting its use in CF.