Acute appendicitis is one of the most common acute surgical conditions of the abdomen. Nevertheless, the indications for appendectomy are associated with a high preoperative rate of false diagnoses. Although the rate of unnecessary appendectomies is comparatively high (20-30%) it is considered acceptable because the rate of perforated appendices is 7-30%. With good availability and lack of radiation exposure, ultrasound is the slice imaging modality of first choice. The sensitivity of ultrasonic detection of appendicitis lies between 55 and 98% and the specificity between 78 and 100%. Computed tomography (CT) has a significantly higher sensitivity for detecting acute appendicitis compared to ultrasound both in infancy and adulthood but the specificity shows no significant differences. CT is, therefore, the imaging modality of choice in cases of relevant differential diagnosis that cannot be visualized adequately or inconclusively by sonography especially in obese and critically ill patients. Comparison of ultrasound and magnet resonance imaging (MRI) revealed a significant advantage for MRI regarding accuracy, sensitivity and negative predictive value. In contrast, specificity and positive predictive value showed no significant differences. Currently MRI is only an alternative imaging modality to ultrasound in cases of undetermined and inconclusive ultrasonic findings especially in childhood and pregnancy. The value of ultrasound in the diagnosis of acute appendicitis is increasing and, particularly in the hands of experienced investigators, is an important imaging modality which delivers important and decision-making findings. Nevertheless, the final decision for appendectomy depends on the findings of the physical examination.