Purpose: Undernutrition is a prevalent problem in older, community-dwelling individuals. Aim of this study was to determine the effects of a dietetic treatment in older, undernourished, community-dwelling individuals. Methods: A parallel randomized controlled trial was performed in 146 non-institutionalized, undernourished individuals aged ≥65 years in primary care. Participants were randomly assigned to the intervention (referral to and treatment by a trained dietitian) or control group (no referral). Body weight, physical performance, handgrip strength, energy intake, protein intake and fat-free mass were assessed at baseline, after 3 months and after 6 months. Results: All randomized participants (n = 146) were included in the intention-to-treat generalized estimating equations analysis (72 in intervention and 74 in control group). No treatment effect was found on the primary outcomes body weight (β = 0.49 kg, 95 % CI: -0.15-1.12), physical performance (β = 0.15 points, 95 % CI: -0.33-0.64) and handgrip strength (β = 0.49 kg, 95 % CI: -0.62-1.60). Furthermore, no treatment effect was found for the secondary outcomes. Predefined subgroup analyses showed a treatment effect on body weight in physically active participants (β = 1.25 kg, 95 % CI: 0.70-2.11) and not in inactive participants (β = -0.20 kg, 95 % CI: -1.16-0.75). Conclusions: After 6 months, a dietetic treatment by trained dietitians does not lead to increases in body weight and physical functioning in older, undernourished, community-dwelling individuals. © 2013 Springer-Verlag Berlin Heidelberg.