PURPOSE: To assess the diagnostic value of color Doppler ultrasonography and power Doppler ultrasonography in the diagnosis of acute appendicitis. MATERIALS AND METHODS: We prospectively reviewed gray scale US, color Doppler US and power Doppler US of the suspected appendicitis of the 107 patients from July 1997 to December 1997. We used chi-square tests as statistical tool. RESULTS: The sensitivity, specificity and accuracy in the diagnosis of acute appendicitis were 83.0%, 96.0%, 86.0% on the gray scale US, 84.0%, 95.8%, 86.0% on the Color Doppler US, and 86.0%, 95.8%, 87.8% on the power Doppler US, respectively. There was no significant statistical difference between them (p=1.000). CONCLUSION: In the diagnosis of acute appendicitis, there was no significant difference in the sensitivity, specificity and accuracy among gray scale US, color Doppler US and power Doppler US. But, color Doppler US and power Doppler US were valuable in the cases that were diagnosed false-negatively on gray-scale US. Diagnosis was easier with power Doppler US than with color Doppler US.