This paper provides evidence-based guidelines for the prescription of activity in the management of non-specific low back pain (NSLBP). The 62 clinical trials published between 1966 and 1997, identified by a search of the Medline and Cinahl databases, were reviewed to provide the basis for the guidelines. The available evidence suggests that physiotherapists should advise patients with acute and sub-acute NSLBP to avoid bed rest and to return to normal activity using time rather than pain as the guide to activity resumption. While structured exercise programs have not been shown to provide a benefit for acute NSLBP, there is strong evidence to support their use for patients with sub-acute and chronic NSLBP and in the prevention of NSLBP.