Purpose Very preterm infants are at risk for cerebellar injury and impaired cerebellar growth with adverse neurodevelopmental outcome. Ultrasound through the mastoid fontanel (MF) with a curved-array or sector probe is the most established method for the sonographic examination of the cerebellum. The goal of our study was to examine the validity of transnuchal ultrasound through the foramen occipitale magnum (FOM) with a linear probe for monitoring postnatal cerebellar growth. Methods Retrospective analysis of routine ultrasound scans through FOM and MF in 105 preterm infants born between 23 and 36 weeks of gestation with a birthweight of less than 1500 g. Results Diameters of the cerebellar hemispheres obtained through the two acoustic windows mastoid fontanel and foramen occipitale magnum showed high correlations (r’s = 0.981 and 0.983, p’s < 0.001). Corrected gestational age was significantly associated with transverse cerebellar diameter (TCD) on the first scan (r = 0.908, p < 0.001) as well as postnatal cerebellar growth (r = 0.920, p < 0.001). Postnatal growth was slightly decreased resulting in cerebellar growth restriction on serial scans. Both associations exceeded the calculated ratio of TCD to head circumference (r = 0.657, p < 0.001) and TCD to biparietal diameter with gestational age (r = 0.705, p < 0.001). Conclusion Transnuchal ultrasound is feasible for examination of the preterm cerebellum and improves image quality compared to scans through the MF with higher resolution at a very short distance. Monitoring cerebellar growth during early postnatal life via transnuchal ultrasound can help to identify children at high risk for neurodevelopmental impairment.