Background : Low food intake is a frequent problem in undernourished hospital patients. Objective : To study whether a reorganization of a hospital catering system enabling patients to choose their evening meal individually, in combination with an increase in the energy density of the food, increases the energy and protein intake of the patients. Design : Observational study comparing the food intake before and twice after the implementation of the new system, the first time by specially trained staff and the second time by ordinary staff members, following training. The amount of food served, eaten and wasted was measured, and energy and protein intake calculated. Results : The quartile of patients with the lowest energy intake consumed on average 128 kJ per patient [(95% confidence interval (CI) 79 178 kJ] with the old system; with the new system they consumed 560 kJ per patient (95% CI 489 631 kJ) on the first occasion, and 1021 kJ per patient (95% CI 939 1104 kJ) on the second occasion. With the old system, the wastage was on average 276 g per patient (48% of the total amount produced) compared with 118 g per patient (30%) and 78 g (21%) on the two test occasions with the new system. Conclusions : Reorganization of a hospital catering system can increase energy and protein intake and reduce waste substantially.