Crohn's disease in the city of Derby, 1951-85. An epidemiological survey of Crohn's disease in the city of Derby showed that the incidence of the condition increased from 0.7/10(5) per year between 1951 and 1955 to 6.67/10(5) per year between 1981 and 1985 but seemed to reach a plateau between 1976 and 1985. Large bowel Crohn's disease was more common in patients presenting aged 60-79 years than in those aged 20-39 years. The increase in incidence was not solely due to the detection of milder disease. There was no evidence that the Asian (Indian subcontinent) population of Derby was resistant to the development of Crohn's disease. 