--London was one of the most rapidly expanding cities in the world in the nineteenth century, but the water supply and sanitary conditions were extremely poor. --In the nineteenth century, there were many theories regarding the causes and spread of epidemic diseases. The miasma theory, which postulated that disease was the result of bad air and odours, was the most popular. --In 1858, as a result of the foul smells from the Thames, the decision was made to improve the sewage system. The new system was first used in 1865, but its actual effect on public health is not clear. --The life expectancy of Londoners did not change in the period 1826-1871, but increased substantially thereafter. In view of this time window, this may have been a result of improvements in the sewage system. --However, it is likely that several other factors, such as improvements in the food and water supply, vaccination programmes, and natural circumstances, were responsible for a large part of this increase.