Objectives-To resolve controversies over associations between a history of middle ear disease and psychosocial or cognitive/ educational outcomes Design-Multipurpose longitudinal birth cohort study. Original cohort comprised all UK births between 5 and 11 April 1970; data were available for approximately 12 000 children at 5 years old and 9000 children at 10 years old. Methods-For 5 year old children, parent reported data were available on health, social, and behavioural factors, including data on two validated markers of middle ear disease. Cognitive tests were administered at 5 and 10 years of age, and behavioural problems rated at 10 years by the child's teacher. Results-After adjustment for social background and maternal malaise, the developmental sequelae of middle ear disease remained significant even at 10 years. The largest eVects were observed in behaviour problems and language test data at age 5, but eVect sizes were modest overall. Implications-These results provide an epidemiological basis for policies that aim to minimise the sequelae of middle ear disease by awareness in parents and preschool teachers, early referral, and intervention for more serious or persistent cases. (Arch Dis Child 1999;80:28-35) Keywords: middle ear disease; behaviour problems; cognitive development; longitudinal study Otitis media with eVusion (OME) or "glue ear" is the most common cause of hearing loss in children; this fluctuating condition can persist in some children, leading to detrimental eVects on behaviour and development. Antisocial behaviour or inattentiveness are consequent on the child's inability to hear, leading to frustration, apparent disobedience, and less use of language as a means to ends. Deficits in speech, language, and behaviour, particularly in children with early onset OME, may lead to reduced cognitive ability. The balance of existing evidence suggests that in most aVected children the developmental and behavioural sequelae of otitis media are short lived and relatively mild.2 Psychosocial and educational outcomes have received less attention than measures of language. Clinical and epidemiological studies suggest some association, but the eVect appears small, and the variability wide, probably because of confounding factors that diVer between various small samples.