Background: Abnormal head shape is an uncommon finding on prenatal ultrasound, often associated with breech presentation, spinabifida, aneuploidy or secondary to oligohydramnios or fetal position. Other aetiologies are rarer and may be more difficult to define. Objective: To determine the aetiology and define management pathways for fetuses with an abnormal skull shape.Methods: Our FMU databases were searched to ascertain all fetuses with an abnormal skull shape. Sonographic findings, diagnosis and outcome were reviewed.Results: Of the 370 cases identified, 31.6% were associated with spinabifida (lemon-shaped), 18.4% with aneuploidy (mostly strawberry-shaped). 19.5% were dolicocephalic, most secondary to fetal position or oligohydramnios (see table). 13 had confirmed craniosynostosis, including thanatophoric dysplasia, Craniofrontonasal dysplasia, Aperts syndrome, Baller-Gerold syndrome, I-cell disease, Muenke craniosynostosis and two with an as yet undefined craniosynostosis syndrome. Overall, 16.5 % had an underlying genetic syndrome.Conclusions: Abnormal fetal head shape may be a normal variant, but is commonly associated with a wide variety of underlying pathologies. In view of the high incidence of genetic syndromes, in the absence of a clear diagnosis, referral to a tertiary centre and genetic input is advised as detection of subtle sonographic features may aid diagnosis, allowing for targeted molecular analysis. An algorithm for management will be proposed.