Blood pressure (BP) is measured in percentiles that are adjusted for sex, age, and height percentile in children and adolescents. Standard tables for the conversion of BP percentiles do not present exact BP percentile cutoffs for extremes in stature, either short (<5th percentile) or tall (>95th percentile). An algorithm can be used to calculate exact BP percentiles across a range of height z scores. We compared values from standard BP tables with exact calculations of BP percentiles to see which were better at identifying hypertension in more than 5,000 children with either short or tall stature. Study subjects were 3-17-year-old patients within HealthPartners Medical Group, an integrated health care delivery system in Minnesota, at any time between 2007 and 2012. Approximately half of the subjects who met the criteria for hypertension using exact calculation would be misclassified as normal using available thresholds in the published BP tables instead of the recommended algorithm, which was not included in the tables.