To date there have been few reports on the impact of dietary intervention on the clinical course of acute shigellosis. Current management of acute shigellosis is primarily focused on antibiotic therapy with less emphasis on nutritional management. In a randomised clinical trial, we examined the role of an energy-dense diet on the clinical outcome in malnourished children with acute dysentery due to shigellosis. Seventy-five children aged 12–48 months with acute dysentery randomly received either a milk–cereal formula with an energy density of 4960 kJ/l (test group) or a milk–cereal formula with energy of 2480 kJ/l (control group) for 10 d in hospital. In both milk–cereal formulas, protein provided 11 % energy. In addition, the standard hospital diet was offered to all children and all children received an appropriate antibiotic for 5 d. The mean food intakes (g/kg per d) in the test and control groups were: 112 (SE 2·28) AND 116 (se 3·48) (P=0·16) on day 1; 118 (se 2·72) and 107 (se 3·13) (P=0·04) on day 5; 120 (se 2·25) and 100 (se 3·83) (P=0·04) on day 10. The mean energy intakes (kJ/kg per d) in the test and control groups respectively were: 622 (se 13·2) and 315 (se 11·3) (P<0·05) on day 1; 655 (se 15·1) and 311 (se 7·98) (P<0·05) on day 5; 672 (se 14·7) and 294 (se 11·1) (P<0·05) on day 10. The food and energy intakes were mostly from the milk–cereal diet. There was no difference between two groups in resolution of fever, dysenteric (bloody and or mucoid) stools, stool frequency and tenesmus. However, vomiting was more frequently observed among the test-group children during the first 5 d of intervention (67 % v. 41 %, P=0·04). There was an increase in the mean weight-for-age (%) in the test group compared with the control group after the 10 d of dietary intervention (6·2 (se 0·6) v. 2·7 (se 0·4), P<0·01). In addition, resolution of rectal prolapse was better (26 % v. 8 %, P=0·04) in the test group v. control group after 5 d, and 13 % v. 6 %, (P=0·08) after 10 d of dietary intervention. Supplementation with a high-energy diet does not have any adverse effect on clinical course of acute shigellosis and reduces the incidence of rectal prolapse in malnourished children.