More than 2,000 persons with developmental disabilities have been transferred from California state institutions into community care in recent years. We investigated whether this has been accompanied by a change in mortality rates, using data on 1,878 clients moved since April 1993. Mortality rates were compared to those expected for comparable persons in institutions. Risk-adjusted mortality rates for movers exceeded institutional rates by 51%, p < .05. After removal of cancer deaths in both groups, this increased to 67%. The effect was largest shortly after the move and in the subjects who had moved most recently. The deinstitutionalization process in California appears to have resulted in a substantial increase in mortality, indicating the need to ensure continuous, consistent, and competent medical care and supervision in the community.