Grunting respirations are recognized as a sign of serious illness in infants and children, but have not been well studied beyond the newborn period. We present three illustrative cases and the results of a descriptive study which elucidates the causes of grunting in infants and children and suggests guidelines for assessing pediatric patients with this symptom. All patients between one month and 18 years of age who presented to the Emergency Department (ED) of The Children's Hospital of Denver during the last five months of 1992 with grunting respirations were prospectively identified, and their charts were retrospectively reviewed. The 51 pediatric patients with grunting respirations (0.3% of all patients seen in the ED) fell into three groups based upon mode of presentation: 1) 55% presented with predominantly respiratory signs and symptoms, and each one had a respiratory or cardiac condition; 2) 25% presented with high fever (greater than 38.5 degrees C) but without respiratory signs and symptoms, and all had an infectious cause (three fourths of them had an invasive bacterial disease); 3) 20% presented with neither fever nor respiratory signs or symptoms and had one of a variety of conditions which appeared to cause pain. Presenting symptoms can guide the selection of tests used to evaluate the infant or child with grunting respirations. Guidelines for evaluation are provided in this report.