Undernutrition is common in surgical patients, is frequently unrecognised and is strongly associated with adverse outcomes such as high rates of complications and mortality, worsening functional status and prolonged hospitalisation. Owing to the associated infection and symptoms such as repeated vomiting, a high prevalence of undernutrition is expected in hydrocephalus patients, which may contribute to their poor surgical outcomes. The aim of this study was to evaluate the influence of preoperative nutritional status on the outcome of Indian patients with hydrocephalus undergoing neurosurgical shunt surgery. One hundred and twenty-four consecutive patients undergoing scheduled hydrocephalus shunt surgery were studied prospectively. All patients underwent nutritional screening according to different parameters prior to surgery. The patients were classified into normally nourished and undernourished groups. The undernourished group was further subdivided into moderately and severely undernourished. The surgical outcome was compared between these groups. A high prevalence (53%) of undernutrition was observed in these patients. Postoperative complications such as shunt infection (P = 0.0023), shunt revision (P = 0.0074) and mortality (P = 0.0003) were significantly more common in undernourished patients compared with normally nourished patients. Serum albumin emerged as the most significant independent predictor of postoperative mortality. The present study demonstrated a high prevalence of undernutrition in hydrocephalus patients in India and its adverse influence on the outcome of shunt surgery. Early preoperative nutritional status screening and its optimisation may decrease the morbidity and mortality of shunt surgery for hydrocephalus. © 2007 The Authors.