Technical Abstract: Measurement of gastrointestinal permeability is commonly used in research and often used clinically. Despite its utility, little is known about sugar excretion timeframes or the potential effects of age and sex on GI permeability testing. We seek to determine the timeframes of sugar excretion and the potential effects of age and sex on urinary recovery of the sugars. Healthy adults and children fasted 4 hours after the evening meal and then ingested a solution of sucrose, lactulose, mannitol, and sucralose. Urine was collected at 30, 60, and 90 minutes after ingestion and then each time the subjects voided during the next 24 hours. Each urine void was collected separately. Median age for the adults was 47.5 years and for children 10 years. There were no differences between children and adults in mean percent dose of sugar recovered. The time of peak urinary recovery of the sugars was generally similar between children and adults. Sucrose urinary recovery declined with age unrelated to sex. Lactulose and sucralose urinary recovery declined with age in females but not in males. Overall, sugar urinary recovery is comparable in children and adults. Specific sugar urinary recovery may change as a function of age and/or sex. These results need to be taken into account when planning and interpreting gastrointestinal permeability studies.