Symptoms of intussusception usually begin suddenly. Typically, symptoms in a child include:

• Irritability. A child may act fussy or uncomfortable and be difficult to soothe.
• Recurring episodes of sudden, severe abdominal pain. During a bout of pain, the child may look pale and may scream and draw up his or her knees. In the early stages, the child may seem normal between bouts of pain, which tend to recur every 5 to 30 minutes and gradually get worse. As the condition progresses, the child becomes weak and listless between episodes of pain.
• Frequent vomiting. As a child's condition gets worse, vomiting decreases. Green fluid in vomit is a sign that the intestine is blocked.
• Passing irregular stools. Early on, stools may appear normal. After a few hours, stools often are smaller but occur more frequently, and diarrhea may develop. About half of children begin to pass bloody stools, usually within about 12 hours to 1 or 2 days of the onset of other symptoms. As the condition progresses, stools may become deep red and also contain mucus, giving them a jelly-like appearance.
• A swollen, tender abdomen. You may be able to feel a mass shaped somewhat like a sausage, usually along the upper right side of the abdomen.

Very few intussusceptions heal on their own. If intussusception is not treated, serious and life-threatening complications can develop, such as infection of the lining of the abdominal wall (peritonitis) or a hole or opening (perforation) in the intestinal wall.

Signs that intussusception is progressing into a serious illness include:

• Shallow breathing and a rapid, weak heartbeat.
• Fever.
• Dehydration.

In adults, the symptoms of intussusception may be less obvious but include vague abdominal pain, nausea and vomiting, abdominal bloating, or a change in the usual stool output, color, or pattern.

Intussusception may sometimes be mistaken for other conditions with similar symptoms, such as a hernia or appendicitis.