Background: Pfeiffer syndrome is associated with a genetic mutation of the FGFR2 (or more rarely, FGFR1) gene, and features the combination of craniosynostosis, midface hypoplasia, broad thumbs and broad great toes. Previous research has identified a wide spectrum of clinical phenotypes in patients with Pfeiffer syndrome. This study aimed to investigate the multifactorial considerations for speech, language, hearing and feeding development in patients with severe geneticallyconfirmed Pfeiffer syndrome.Methods: A 23-year retrospective case-note review of patients attending the Oxford Craniofacial Unit was undertaken. Patients were categorized according to genotype. Patients with mutations located in FGFR1, or outside the FGFR2 IgIII domainhotspot, or representing known Crouzon/Pfeiffer overlap substitutions were excluded. Twelve patients with severe FGFR2-associated Pfeiffer syndrome were identified.Results: Patients most commonly had pansynostosis (n=8) followed by bicoronal (n=3), and bicoronal and sagittal synostosis (n=1). Seven patients had a Chiari I malformation. Four patients had a diagnosis of epilepsy. Ten patients had with hydrocephalus necessitating ventriculoperitoneal shunt insertion.Feeding difficulties were common (n=10/12) and multifactorial. In 5/12 cases, they were associated with pansynostosis, hydrocephalus, tracheostomy and tube feeding in infancy.Hearing data were available for 10 patients, of whom 9 had conductive hearing loss, and 8 required hearing aids. Results indicated that 3/4 patients had expressive language difficulties, 3/4 had appropriate receptive language skills. 6/12 patients had a speech sound disorder and abnormal resonance. Conclusion:This study has identified important speech, language, hearing and feeding issues in patients with severe FGFR2-associated Pfeiffer syndrome. Results indicate that a high rate of motor-based oral stage feeding difficulties, and pharyngeal stage swallowing difficulties necessitating regular review by specialist craniofacial speech and language therapists