The proportions of all registered patients in the General Practice Research Database who received asthma treatment in 1996 were highest in children, lowest in middle age and rose again in the elderly, with the prevalence in men almost doubling between ages 50 and 75. Some of this rise in the elderly may be due to chronic obstructive airways disease diagnosed as asthma, rather than true late onset asthma. In children and younger adolescents (ages 5-15), treated asthma was more common in boys than in girls, which is compatible with findings in recent population surveys of school children. From mid-adolescence until around age 75, treated asthma was more common in women.