Acute acalculous cholecystitis is uncommon in pediatrics and more likely to be encountered in adult patients. Signs and symptoms of acute cholecystitis are similar to other causes of acute abdominal pain such as pancreatitis, gastritis, and acute appendicitis, further making diagnosis difficult. We present a case of acute acalculous cholecystitis in a child with cystic fibrosis and discuss the role of emergency physician bedside sonography in the evaluation of right-upper-quadrant pain.