AbstractGene variants that dysregulate signaling through the RAS‐MAPK pathway cause cardiofaciocutaneous syndrome (CFCS), a rare multi‐system disorder. Infantile epileptic spasms syndrome (IESS) and other forms of epilepsy are among the most serious complications. To investigate clinical presentation, treatment outcomes, and genotype–phenotype associations in CFCS patients with IESS, molecular genetics and clinical neurological history were reviewed across two large clinical research cohorts (n = 180). IESS presented in 18/180 (10%) cases, including 16 patients with BRAF variants and 2 with MAP2K1 variants. Among IESS patients with BRAF variants, 16/16 (100%) had sequence changes affecting the protein kinase domain (exons 11–16), although only 57% of total BRAF variants occurred in this domain. Clinical onset of spasms occurred at a median age of 5.4 months (range: 1–24 months). Among 13/18 patients whose IESS resolved with anti‐seizure medications, 10 were treated with ACTH and/or vigabatrin. A substantial majority of CFCS patients with IESS subsequently developed other epilepsy types (16/18; 89%). In terms of neurodevelopmental outcomes, gross motor function and verbal communication were more limited in patients with a history of IESS compared to those without IESS. These findings can inform clinical neurological care guidelines for CFCS and development of relevant pre‐clinical models for severe epilepsy phenotypes.