Introduction: The diagnosis of acute appendicitis (AA) is usually clear cut but sometimes there is atypical presentation of this condition in children. There is a need to determine and compare the diagnostic accuracy of these three pre-operative diagnostic modalities: Paediatric Appendicitis Score (PAS), abdominal ultrasonographic scan (USS) findings, and serum C-reactive proteins (CRPs). The objective of this study was to determine the diagnostic accuracy of the three diagnostic modalities and to compare each diagnostic test result with the histopathological results of the appendix specimens. Materials and Methods: This was a prospective cross-sectional study that involved children aged 4–15 years with suspected AA who presented at the emergency paediatric unit of a tertiary health care hospital in North Central, Nigeria. The PAS, quantitative serum CRP, and abdominal USS were performed for all eligible patients. Results: A total of 43 patients were included in this study. Forty appendicectomy specimens (93%) were histologically confirmed to be AA and three appendicectomy specimens (7%) were normal appendix. The diagnostic accuracy values of PAS, abdominal USS, and CRP were 95.3%, 93.0%, and 90.7%, respectively. Conclusion: This study demonstrated that PAS, abdominal USS, and serum CRP provided useful diagnostic accuracy for AA in children.