Calprotectin has been proposed as a useful marker of inflammatory bowel disease in children. We did a pilot study to establish whether it can be used to aid diagnosis of necrotising enterocolitis in preterm infants. Patients with clinical features of necrotising enterocolitis had raised faecal calprotectin concentrations at the time of diagnosis compared with matched controls (288.4 mg/L [SD 49.1] and 98.0 mg/L [60.6], respectively; p=0.0006). Faecal calprotectin might be a useful marker of gastrointestinal mucosal inflammation in neonates.