[en] A mucous membrane of the maxillary sinus is clinically important in the dental fields. Magnetic resonance imaging (MRI) can demonstrate a mucous membrane because the mucosa contains rich free water. However, the morphology and location of the mucous membrane of normal maxillary sinuses have not been studied well by MRI. T2-weighted coronal images were obtained by spin echo technique in 40 normal volunteers. The eight maxillary sinuses were classified into four groups (Type 1∼IV) according to the morphology and also classified into five groups (Type a, b1, b2, b3, c) according to the location of the mucous membrane. Coronal images obtained at a standard angle of 77 degree to the Frankfort horizontal (FH) plane was the best for the evaluation of maxillary sinus because the image displayed the maximum cross-section of the maxillary sinus. In the normal cases, Type I (no high signal intensity) was observed in 20 sites, Type II (linear high signal intensity) in 48 sites, Type III (belt-like high signal intensity) in 11 sites and Type IV (mass-like high signal intensity) in 1 site. Type a (medial∼basal wall) was observed in 46 sites, Type b1 (medial wall alone) in 4 sites, Type b2 (basal wall alone) in 8 sites and Type c (entire wall) in 2 sites. Half of the cases showed the same findings bilaterally. Thus, MRI could demonstrate the morphology and location of the mucous membrane in the normal maxillary sinus so clearly that MRI was considered to be a useful diagnostic tool in the dento-maxillo-facial region. (author)