The objectives of this paper were to identify gestational age-independent parameters for cerebellar vermis (CV) evaluation and examine their use in CV integrity assessments. Using three-dimensional ultrasonography, we obtained the following measurements from 217 pregnant women carrying 18-37-week-old fetuses: the largest area of the CV, vermal craniocaudal distance (VCC), vermal anterior to posterior diameter, and vermal perimeter (VP). In addition, fetal growth parameters (biparietal diameter, head circumference femoral length [FL], humeral length, transverse cerebellar diameter, and abdominal circumference) were evaluated. The ratios of the CV dimensions to each other and to the fetal growth parameters were calculated. Ratios showing no significant correlation with gestational age and acceptable internal validity in subsequent bootstrap analyses were chosen. The normal ranges of the specific parameters were compared with cases identified with posterior fossa anomalies (PFA). The ratios VP/FL (mean 1.20, SD 0.09), VCC/FL (mean 0.36, SD 0.03), and VCC/VP (mean 0.3, SD 0.03) were chosen using our protocol. These parameters were not significantly different between normal fetuses and those with PFA and an intact vermis. However, VP/FL and VCC/FL values were abnormal in cases of hypoplastic vermis or vermian agenesis, while the VP/VCC value was abnormal only in cases of vermian agenesis. The VP/FL, VCC/FL, and VCC/VP ratios are gestational age-independent parameters in evaluation of CV integrity.