Objective. To review the prenatal development of the maxillary sinus under the perspective of the sinus surgery. Study Design. Cross-sectional study. Setting. Basic embryology laboratory. Subjects and Methods. Morphometry and morphology of the maxillary sinus and its ostium were studied under stereomicroscopy in 100 human fetuses from the 9th to the 37th week. Fetuses were obtained from the Fetal Collection of the School of Medicine of the Universidad Autonoma de Nuevo Leon. Approval was granted by the Ethics Committee. Statistics were applied. Results. The maxillary sinus begins its development at the 10th week. On the 37th week, the anterior-posterior diameter has a mean of 4.36 mm; ossification of the medial wall was absent, and the floor was located below the attachment of the inferior turbinate. Septa and recesses were temporarily observed. Some variations in shape were observed; however, only the oval shape persisted. Maxillary sinus hypoplasia was not found, although asymmetry was present in 30% of cases. The ostium was located at the anterior third of the ethmoid infundibulum; its final dimensions were 1.96 mm in length and 0.44 mm in width. The mean length between the ostium to the lamina papyracea and nasolacrimal duct was 1 mm. One case of double maxillary sinus was observed. Significant difference between the variables, in accordance with the age, was found (P = .02). Conclusion. Knowledge of prenatal development of the maxillary sinus improves the perspective of the sinus surgeon and helps the understanding of postnatal anatomy, especially in children.