This document describes the development of a computable phenotype for Crohn's disease using data from the PEDSnet network. It discusses defining case and non-case definitions using various combinations of diagnoses, medications, procedures. It then evaluates the phenotype algorithms through internal validation of consistency across sites and predictive ability compared to procedures, and external validation against a gold standard of manually curated cases. The key lessons are on the importance of evaluating data quality issues across sites and balancing sensitivity vs specificity in selecting the final algorithm.