The UK National Study of Hearing set out to ascertain the prevalence of hearing impairments of various magnitudes, the prevalence of ear disease and the associated risk factors, and to estimate the percentage of individuals requiring some form of management. A stratified sample of 2708 British adults, aged 18-80 years, was chosen from a sample of 48,313 adults, randomly selected from the electoral roll, for a full otological and audiological assessment. This paper deals primarily with the middle ear results. Otoscopically, 2.6% of British adults had inactive and 1.5% had active chronic otitis media. This condition was more common in older individuals and in those in manual occupations. For this purpose, presumptive otosclerosis was defined as a conductive component to the impairment (average air bone gap over 0.5, 1 and 2 kHz of 15 dB or greater) and with an intact tympanic membrane. The population prevalence for presumptive otosclerosis was 2.1%, for healed OM 1.7% and for Eustachian tube dysfunction 0.9%. This prevalence of otosclerosis was higher in those over 40 years, but only in those with air bone gaps of 30 dB or greater were women more likely to have the condition than men, by a factor of three. At most, 20% of individuals with any of the above middle ear conditions will have had ear surgery.