The Ras-RAF-mitogen-activated protein kinase (Ras-RAF-MAPK) pathway is overactive in many cancers and in some developmental disorders. In one of those disorders, namely, Noonan syndrome, nine activating C-RAF mutations cluster around Ser259, a regulatory site for inhibition by 14-3-3 proteins. We show that these mutations impair binding of 14-3-3 proteins to C-RAF and alter its subcellular localization by promoting Ras-mediated plasma membrane recruitment of C-RAF. By presenting biophysical binding data, the 14-3-3/C-RAFpS259 crystal structure, and cellular analyses, we indicate a mechanistic link between a well-described human developmental disorder and the impairment of a 14-3-3/target protein interaction. As a broader implication of these findings, modulating the C-RAFSer259/14-3-3 protein-protein interaction with a stabilizing small molecule may yield a novel potential approach for treatment of diseases resulting from an overactive Ras-RAF-MAPK pathway.