Objectives: To evaluate the effect on the process of care of an active strategy to implement clinical guidelines on physiotherapy for low back pain. Design: A cluster randomised controlled trial comparing an active strategy with standard dissemination. Setting: Primary care physiotherapy practices. Participants: 113 physiotherapists were randomly allocated to receive the guidelines by mail (control group) or to receive an additional active strategy (intervention group) which consisted of a multifaceted programme including education, discussion, role playing, feedback, and reminders. Main outcome measures: Adherence to the guidelines was measured by means of individual patients' forms recording the treatment completed by the physiotherapist. The forms were assessed using an algorithm based on the number of treatment sessions, treatment goals, interventions, and patient education. Results: Physiotherapists in the intervention group more often correctly limited the number of treatment sessions for patients with a normal course of back pain (OR 2.39; 95% CI 1.12 to 5.12), more often set functional treatment goals (OR 1.99; 95% CI 1.06 to 3.72), more often used mainly active interventions (OR 2.79; 95% CI 1.19 to 0.55), and more often gave adequate patient education (OR 3.59; 95% CI 1.35 to 9.55). They also adhered more to all four criteria (OR 2.05; 95% CI 1.15 to 3.65). Conclusions: The active strategy moderately improved adherence to the guidelines. Active strategies are recommended to implement the clinical guidelines on physiotherapy for low back pain.