This preprint introduces the “Flat Foot” Hypothesis in Autism, proposing that, in some individuals with ASD, pes planus may function as an adaptive somatopsychological compensation to stabilize posture and cope with sensory load. The article integrates biomechanical reasoning, clinical observations, and a focused review of peer-reviewed studies reporting higher flat-foot prevalence in ASD than in neurotypical controls. It outlines testable predictions, alternative explanations (e.g., hypotonia, connective-tissue differences), and clinical implications, emphasizing function-before-form and individualized assessment (e.g., baropodometry) before reflex orthopedic correction. The goal is to reframe flat feet in ASD from a purely orthopedic deficit to a potential self-regulatory strategy, pending empirical validation. License: CC BY 4.0. Author ORCID: 0009-0004-0747-0117.