Background: Appendicitis is the most common surgical emergency in children, yet diagnosis of equivocal presentations continues to challenge clinicians. Aim: The objective of this study was to investigate the hypothesis  that the use of a modified clinical  practice and harmonic ultrasonographic grading scores (MCPGS)  may improve the accuracy in diagnosing acute appendicitis in the pediatric population. Patients & methods: Main outcome measures: Sensitivity,  specificity, and accuracy ofthe modified scoring system. Five hundred and thirty patients presented with suspected diagnosis of acute appendicitis during the period from December 2000 to December 2009 were enrolled in this study. They were classified into 2 equal groups. Group I (n=265): Included  children who presented with suspected diagnosis of acute appendicitis. To these children a special clinical practice guideline system (CPGS) incorporating clinical judgment and results of gray scale US was applied),2 Group II (n=265): Included a similar group of children with equivocal diagnosis of acute appendicitis (AA), to whom a modified clinical practice guideline system (MCPGS) was applied. Statistical analyses were carried out using Z test for comparing 2 sample proportions and student's t-test to compare the two quantitative data in both groups.Sensitivity and specificity for the 2 scoring systems were calculated using Epi-Info software. Results: The Number of appendectomies declined from 200 (75.5%) in group I to 187 (70.6%) in group II (P>0.05). Specificity was significantly  higher when applying MCPGS (90.69%) in group II compared to 70.47% in group I when CPGS was applied (P<0.01). Furthermore, the PPV was significantly higher in group II (95.72%) than in group I (82.88%) (P <0.01). Conclusions: MCPGS tends  to reduce the numbers of avoidable and unnecessary appendectomies in suspected  cases of pediatric  acute appendicitis that may help in saving hospital resources.