In recent years, plain X-ray CT has often been the first choice for imaging examination of acute abdomen in emergency medical settings. Ultrasound examination depends on the skill of the operator and the findings are subjective. However, we often experience cases in which more information can be obtained by abdominal ultrasonography than by plain CT. In this report, we describe two cases in which ultrasonography and plain CT imaging were performed in patients with right lower abdominal pain due to suspected abscess formation around the cecum. In the future, policies to reduce medical costs such as community healthcare initiatives may progress, and the number of facilities with high-priced medical equipment such as X-ray CT may decrease. Ultrasonography provides more information than simple CT examination, so we believe that ultrasonography should be the first choice for diagnostic imaging of acute abdomen. Therefore, it is important for those involved in ultrasonography to continuously acquire knowledge and scanning techniques.