To study the fetal morphogenesis of the lateral nasal wall and nasal conchae as well as the initial development of the paranasal sinuses, 15 specimens were investigated. Their crown-rump lengths ranged from 25 to 263 mm. The specimens were fixed in Bouin's solution. Serial sections were stained with hematoxylin and eosin, and Mallory's trichrome stain. The objectives were to ascertain the time and course of development of: (1) ossification in the maxilla and palate, (2) formation of the nasal capsule and the conchae, (3) chondrification and ossification in the nasal capsule and conchae, (4) the maxillary sinus and ethmoidal cells, and (5) glands in the respiratory mucosa. The earliest appearance of the conchae was observed in a 25 mm CR fetus. In a 32 mm CR fetus, ossification in the maxilla and palate was begun and the first maxillary sinus primordium was observed. The glands associated with the maxillary sinus and the inferior concha developed in a 49 mm and in a 90 mm CR fetus, respectively. The ethmoid and three conchae started to ossify in a 160 mm CR fetus. It was concluded that the transformation of mesenchyme into the bony skeleton was accomplished in a 263 mm CR fetus. Both groups of paranasal sinuses and the respiratory glands in the 263 mm CR fetus were morphologically well differentiated. In addition to an extensive survey of the literature, the possible role of the mucosal glands in development of the paranasal system was discussed.