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338 a recent study among children aged 8-18 years, it has been shown that in children verbal report and evaluation of stool consistency according to the BSFS also strongly differ. 27 In an attempt to create a reliable and age-appropriate assessment tool for stool consistency assessment in infants and toddlers, the Brussels Infant and Toddler Stool Scale (BITSS) was developed. 28 In chapter 6 , we describe a study on interrater reliability of this new visual stool form scale among 1,181 parents, 624 nurses and 657 physicians from 18 countries. We concluded that the BITSS shows moderate agreement with the BSFS and that after grouping BITSS photographs together, this visual stool form scale is likely to prove useful in the assessment of stools of non-toilet trained children. A gold standard for stool consistency assessment is not available and more clinical studies involving assessment of fresh stools using the BITSS are required to demonstrate its usefulness in clinical practice and for research purposes. In chapters 7 and 8 we describe findings from colonic manometry studies in children with intractable FC. Colonic manometry enables assessment of colonic motor patterns and is increasingly utilized in the evaluation of intractable constipation in children. Since the introduction of high-resolution colonic manometry catheters, more detailed information on colonic motor patterns has become available. However, published data on high-resolution colonic manometry in children remain scarce. In chapter 7 , we describe results from 18 children with FC who underwent water-perfused colonic manometry with a catheter containing 36 channels, spaced 1.5 cm apart. These results were compared with previously published data from healthy adults and adults with slow transit constipation, obtained with a fiber-optic manometry catheter. 29,30 We concluded that children with FC show an impaired postprandial colonic response similar to adults with slow transit constipation. However, since these results were acquired with water-perfused colonic manometry, we could not rule out whether water infusion into the colon could have influenced our results. Therefore, in chapter 8 , we performed a similar study. Only this time, we included patients who had undergone solid state colonic manometry (36 sensors, 3 cm apart), where no water infusion into the colon occurs. Again, we found similar results, indicating that the postprandial meal response seen in healthy adults is diminished in patients with FC. As this postprandial meal response is likely to be mediated via extrinsic neural input, these findings support the hypothesis that an extrinsic neuropathy may play a role in children with intractable FC. 31 Moreover, we demonstrated that long single motor patterns are frequently observed in children with FC. Interestingly, these motor patterns have been described in vivo , but they are more commonly recorded in intact sections of human colon ex vivo in an organ bath. 29,30,32 This could indicate that these motor patterns are normally suppressed in vivo when extrinsic input to the colon remains intact and their common occurrence in children with FC may support our hypothesis of an extrinsic neuropathy. 32 Age-related changes in colonic motility have been described. 33 Therefore, a major limitation in both studies was the