Objective: This study examines an thropometric specifications of mentally retarded children with microcephalia, macrocephalia, and idiopathic etiology, and comparing them with normal children. Method: For this field study, 15 subjects were selected for each group. For measuring the specifications we used balance, meter, and caliper. Results: The ANOVA and Sheffé post hoc tests analysis displayed significant differences in physical indications in the groups such as weigh, sitting and standing position size, circumference of head, width and length of nose, and some other features. Conclusion: These results suggest significant differences in the physical characteristics in children with different etiologies. Clinical implications and related limitations have been discussed.