[Normal pneumatization time of paranasal sinuses in 799 children: evaluation with magnetic resonance imaging]. 
To evaluate the onset of initial pneumatization of paranasal sinuses with magnetic resonance imaging (MRI) and provides references in the diagnosis and treatment of pediatric paranasal sinuses disease.  The MRI images of paranasal sinuses were retrospectively reviewed for 799 children of 0 month to 15 years old and the first pneumatization time of paranasal sinuses were analyzed.  The ethmoidal sinuses was the first pneumatized in 100% (46/46) of newborn children.  And 45.7% (21/46) of maxillary sinuses showed pneumatization during the first month of life and 97.8% (45/46) were pneumatized at 7 - 12 months.  The pneumatized sphenoid sinuses was first identified as early as 4 months.  And 86% (43/50) were pneumatized from 1 to 2 years old.  Frontal sinuses was the last pneumatized paranasal sinuses.  And 8% (4/50) of frontal sinuses were pneumatized at 1 - 2 years old and 97.8% (42/43) showed pneumatization at 14 - 15 years old.  MRI may be used to observe the pneumatization of paranasal sinuses.  The initial pneumatization time of paranasal sinuses is earlier than previously described.