Objective: To perform a systematic review evaluating the value of abdominal radiography, colonic transit time (CTT), and rectal ultrasound scanning in the diagnosis of idiopathic constipation in children. Study design: Eligible studies were those assessing diagnostic accuracy of abdominal radiography, CTT, or rectal ultrasound scanning in children suspected for idiopathic constipation. Methodological quality of the included studies was assessed with the Quality Assessment of studies of Diagnostic Accuracy included in Systematic reviews checklist. Results: One systematic review summarized 6 studies on abdominal radiography until 2004. The additional 9 studies evaluated abdominal radiography (n = 2), CTT (n = 3), and ultrasound scanning (n = 4). All studies except two used a case-control study design, which will lead to overestimation of test accuracy. Furthermore, none of the studies interpreted the results of the abdominal radiography, ultrasound scanning, or CTT without knowledge of the clinical diagnosis of constipation. The sensitivity of abdominal radiography, as studied in 6 studies, ranged from 80% (95% CI, 65-90) to 60% (95% CI, 46-72), and its specificity ranged from 99% (95% CI, 95-100) to 43% (95% CI, 18-71). Only one study presented test characteristics of CTT, and two studies presented test characteristics of ultrasonography. Conclusion: We found insufficient evidence for a diagnostic association between clinical symptoms of constipation and fecal loading on abdominal radiographs, CTT, and rectal diameter on ultrasound scanning in children. Copyright © 2012 Mosby Inc. All rights reserved.