BackgroundSelf-management support is an important component of the clinical management of many chronic conditions. The validated Self-Management Screening questionnaire (SeMaS) assesses individual characteristics that influence a patient’s ability to self-manage.AimTo assess the effect of providing personalised self-management support in clinical practice on patients’ activation and health-related behaviours.Design and settingA cluster randomised controlled trial was conducted in 15 primary care group practices in the south of the Netherlands.MethodAfter attending a dedicated self-management support training session, practice nurses in the intervention arm discussed the results of SeMaS with the patient at baseline, and tailored the self-management support. Participants completed a 13-item Patient Activation Measure (PAM-13) and validated lifestyle questionnaires at baseline and after 6 months. Data, including individual care plans, referrals to self-management interventions, self-monitoring, and healthcare use, were extracted from patients’ medical records. Multilevel multiple regression was used to assess the effect on outcomes.ResultsThe PAM-13 score did not differ significantly between the control (n= 348) and intervention (n= 296) arms at 6 months. In the intervention arm, 29.4% of the patients performed self-monitoring, versus 15.2% in the control arm (effect sizer= 0.9,P= 0.01). In the per protocol analysis (controln= 348; interventionn= 136), the effect of the intervention was significant on the number of individual care plans (effect sizer= 1.3,P= 0.04) and on self-monitoring (effect sizer= 1.0,P= 0.01).ConclusionThis study showed that discussing SeMaS and offering tailored support did not affect patient activation or lifestyle, but did stimulate patients to self-monitor and use individual care plans.