The effects of cognitive and physical decline on changes in the size and composition of four types of personal networks over a period of six years were investigated in a Dutch sample of 1552 older adults, aged 55-85 years. The effects of age and a decline in cognitive and physical functioning on the probability of changes in all possible network types were investigated. Transitions related to age and to cognitive and physical decline were observed for about one-third of the study sample. Greater age was associated with an increase in the number of family members in the network. Physical decline was associated with a replacement of friends and neighbors by family members only if the network was large. In small networks, no such association occurred. Cognitive decline was associated with a loss of relationships, most likely friends and neighbors, who were not found to be replaced by family members. Physical decline appears to be associated with an increase in the potential number of supporters in the network, whereas cognitive decline is associated with a decrease in the number of potential supporters.