Objectives.To evaluate the effect of unilateral nasal obstruction (by nasal polyps of different histopathology) on olfactory bulb volume using MRI technique. Study Design.Cross-sectional study. Setting.Tertiary university hospitals, Departments of Otolaryngology and Subjects and Methods.Eleven patients with a few months of complete unilateral nasal obstruction of different pathological etiologies were selected. MRI assessment of olfactory bulb volume was performed using planimetric manual contouring.The contralateral olfactory bulb was used as a comparative control for the same patient. Eleven healthy controls constituted the control group. Results.Mean olfactory bulb volume ± SD of obstructed side =14.3 ± 3.7 mm3, mean olfactory bulb volume ± SD of nonobstructed side = 43.49 ± 10.7 mm3. The difference between the 2 sides was significant (P = .003). The difference in olfactory bulb volume between normal subjects and nonobstructed nasal side was statistically nonsignificant (t = .9118, P = .3727), while the difference between normal subjects’ olfactory bulb volume and obstructed nasal side olfactory bulb volume in our patients was extremely statistically significant (t = 9.7320, P >.0001). A strong negative correlation was found between duration of obstruction and olfactory bulb volume (R = 20.9761). Conclusion. This study shows that unilateral nasal obstruction may be associated with a lateralized ipsilateral difference of olfactory bulb volume.