Background: Gestational age (GA) is an important parameter in obstetrics for management of pregnancy and evaluating fetal development. High incidence of perinatal mortality has been noted in patients whose accurate gestational age is not known. Objective: The aim of this study was to evaluate whether trans-cerebellar diameter (TCD) in singleton gestations can serve as a reliable predictor of gestational age (GA) in fetuses in the second and third trimester between 14-40 weeks of pregnancy in women attending the clinic for routine ultrasound examination. Patients and methods: This prospective study was carried out at the antenatal outpatient clinic at Al-Zahraa university Hospital and El-Sahel Teaching Hospital. This study was hold one thousand of pregnant women attending the outpatient clinic for routine ultrasound examination during second and third trimester between 14-40 weeks of pregnancy in a period from 1 December 2016 to March 2019. Patients and methods: This prospective study included a total of one thousand of pregnant women, attending at Antenatal Outpatient Clinic, Al-Zahraa University Hospital and El-Sahel Teaching Hospital. The accuracy of the transverse Cerebellar Diameter (TCD) in the prediction of gestational age (GA) in fetuses in the second and third trimester between 14-40 weeks of pregnancy was assessed. This study was conducted between December 2016 to March 2019 Results: According to accuracy of measured gestational age according to measured parameters in relation to actual gestational age (accuracy within 2 weeks), TCD had the highest accuracy (98.7%) than other parameters in early second trimester. Accuracy of TCD in late second trimester was 91.6% and 82% in early third trimester while in late third trimester TCD had the lowest accuracy (68.1%). Conclusion: TCD is an accurate parameter in estimation of gestational age as its values are in close relation with that of GA by LMP. TCD is a better predictor of the gestational age when compared to other parameters especially between (14-22) weeks.