Middle ear fluid is a common problem in children. Eustachian tube dysfunction has been considered the key to the pathogenesis of this disorder, but new studies show that other factors may be operative. Inflammation appears to play a significant role in high-viscosity effusion, and these effusions may be related to acute suppurative otitis media. Since persistent mild hearing loss may adversely affect verbal development, new emphasis on early treatment of middle ear effusion is warranted.