Abdominal pain is the main symptom of appendicitis. The pain starts out as diffuse, meaning it is difficult to localize the area of pain. Most people say the initial pain of appendicitis occurs around the middle portion of the abdomen. As the inflammation of the appendix progresses, the pain becomes localized to one area. Once the peritoneum (lining tissue of the abdomen) is inflamed, the pain of appendicitis is characteristically located at a point between the navel and the front of the right hip bone. Anatomically, this is referred to as McBurney's point. Another frequent symptom of appendicitis is loss of appetite. Over time, this can worsen, resulting in nausea and vomiting. Other symptoms that can occur are swelling of the abdomen, the inability to pass gas, constipation or diarrhea with gas, and a mild to moderate fever. Some people with appendicitis have atypical symptoms. They may not have the classic pain localized in the lower right abdomen. Sometimes, affected people report experiencing pain in the lower back or rectum. Painful urination has also been reported. The nausea and vomiting may precede the onset of abdominal pain in certain cases.