In many pregnant women, it is very difficult to accurately assess the fetal gestation age, due to pregnancy on top of lactation or contraceptive method, unsure of date, irregular cycles, late booking and missing the dating scan. Therefore, we might have a wrong diagnosis of preterm or postterm pregnancy, which will affect the outcome of pregnancy. Patients and methods: In our prospective study, we examined 70 normal pregnant women and 70 intrauterine growth restricted (IUGR) pregnancy cases after Ethical Committee approval and informed written consent, to assess the effectivity of transcerebellar diameter (TCD) in detection the age of gestation in normal pregnancy and IUGR cases in relation to other ultrasound parameters as biparietal diameter (BPD), head circumference (HC), femur length (FL), abdominal circumference (AC). In addition, TCD/AC ratio was assessed for its efficiency in diagnosing IUGR pregnancy if its value was above 95^th percentile. Results: Our results showed no significant difference between the mean gestation age detected by TCD compared to the actual mean gestation age in normal as well as IUGR cases, in addition the TCD showed the highest diagnostic accuracy of 95% in detection of gestation age in IUGR within 2 weeks. TCD/AC ratio showed accuracy of 91.43% in diagnosis of IUGR if ratio above 95^Th percentile. Conclusion: TCD is a very important parameter in diagnosis of IUGR cases and proper assessment of gestation age.