This article focuses on the increase of long term contributory sickness benefits in the insured populations in Great Britain. The growth in the number of claimants of long term contributory sickness benefit is something of a puzzle. Some obvious explanatory candidates, such as the growth of unemployment, changes in the real value of benefits, and the aging of the population, as well as other potential variables, are introduced in the context of time series analysis. In the aggregate time series analysis, the number of Invalidity Benefit claimants in each financial year from 1962-63 to 1989-90 was regressed on the unemployment rate and various measures of the real value of Invalidity Benefit. A range of characteristics determine the probability of Invalidity Benefit receipt in the Probit analysis. Age might be expected to have an impact on the probability of Invalidity Benefit receipt, both because of the greater incidence of long-term illness associated with the aging process, and the relationship between early retirement, discouraged worker effects and benefit receipt. Health status is also expected to have an impact on probability of receipt of Invalidity Benefit. Housing tenure may have an impact both on health status directly and may also signal underlying differences in income. The local unemployment rate may also have an effect on the probability of Invalidity Benefit receipt, where higher unemployment induces a withdrawal from the labor market through a discouraged worker effect.