The association between hearing impairment in adolescence and school performance and the outcome of education was studied among 25-year-old subjects followed since pregnancy in the Northern Finland birth cohort. The series, 395 subjects with abnormal hearing and 977 randomly selected controls, was based on a questionnaire on hearing and school achievement sent to 11780 members of the cohort alive at the age of 14 years, and on audiometric screening test requested from health centers. Hearing loss was defined as 'clinically significant' if the pure tone average (PTA; mean of the thresholds at 0.5, 1 and 2 kHz) exceeded 25 dB in the better ear; a threshold of > or = 30 dB at 4 kHz and a PTA of < or = 25 dB as '4 kHz loss'; and as 'slightly abnormal' if any of the thresholds exceeded 20 dB at any frequency and the case did not belong to the above two categories. The more severe the hearing impairment, the poorer was the child's performance at elementary school. Those with normal hearing and those with a slightly abnormal or 4 kHz loss were equally often accepted for intermediate education (88%), while those with a clinically significant loss had the lowest acceptance figures (64%). When adjusting for neurological and social confounders, excluding mental disability, the risk of not qualifying from intermediate or higher education at all was twice as high among those with a clinically significant loss as among the controls (OR 2.1, 95% CI 1.13-3.8), and was still elevated after adjustment had been made for all the relevant perinatal, neurological and social factors (OR 1.9, 95% CI 1.02-3.6). 14% of those with a clinically significant hearing loss, 9% of the subjects with a 4 kHz loss and 7% of those with normal hearing were unemployed at the age of 25 years. Hearing impairment appears to have effects on both the outcome of education and employment status.