The development of the paranasal sinuses, in human race and in many mammals remained as much an enigma as it did nearly two millennia ago. Morphometric analysis of maxillary sinuses in human foetuses are not fully documented and also their morphological studies in Indian population are non-existent. So the present study was conducted to determine the different diameters, the pattern of growth, sexual dimorphism and bilateral variations in maxillary sinuses. 37 human foetuses of different age groups (16-34 wks of IUL) were divided into five groups on the basis of age. Maxillary sinuses were dissected out from the nasal aspects of maxillae and their various diameters were measured with the help of Vernier callipers. The percent growth of AP diameter was +48% in 17-20 wks (p <0.001), of vertical diameter was +60% in 17-20 wks (p <0.001) and of transverse diameter was + 47% in 17-20 wks (p <0.001). Out of 3, anteroposterior diameters were maximum throughout foetal life. AP diameters of both sides of a foetus had significant variation (p <0.005) in <17 wks. AP diameters were invariably more in males but significant variation (p <0.001) was found only in 26-36 wks while significant variation (p <0.02) was observed in transverse diameters in males of 21-25 wks. Anteroposterior dimensions showed faster growth while other diameters were in pace with the head circumference. It was concluded that: 1) Different diameters of maxillary sinus have spurt of growth in different periods of IUL. 2) Values of anteroposterior diameter remain higher, right from the beginning to the end of intra-uterine life. 3) Maxillary sinuses remain relatively larger in males throughout life.