Objective To evaluate whether an interdisciplinary primary care approach for community dwelling frail older people is more effective than usual care in reducing disability and preventing (further) functional decline. Design Cluster randomised controlled trial. Setting 12 general practices in the south of the Netherlands Participants 346 frail older people (score >= 5 on Groningen Frailty Indicator) were included; 270 (78%) completed the study. Interventions General practices were randomised to the intervention or control group. Practices in the control group delivered care as usual. Practices in the intervention group implemented the "Prevention of Care" (PoC) approach, in which frail older people received a multidimensional assessment and interdisciplinary care based on a tailor made treatment plan and regular evaluation and follow-up. Main outcome measures The primary outcome was disability, assessed at 24 months by means of the Groningen Activity Restriction Scale. Secondary outcomes were depressive symptomatology, social support interactions, fear of falling, and social participation. Outcomes were measured at baseline and at 6, 12, and 24 months' follow-up. Results 193 older people in the intervention group (six practices) received the PoC approach; 153 older people in the control group (six practices) received care as usual. Follow-up rates for patients were 91% (n=316) at six months, 86% (n=298) at 12 months, and 78% (n=270) at 24 months. Mixed model multilevel analyses showed no significant differences between the two groups with regard to disability (primary outcome) and secondary outcomes. Pre-planned subgroup analyses confirmed these results. Conclusions This study found no evidence for the effectiveness of the PoC approach. The study contributes to the emerging body of evidence that community based care in frail older people is a challenging task. More research in this field is needed.