While integration has become a central tenet of community-based care for frail elderly people, little is known about its impact on formal and informal care and their dynamics over time. The aim of this study was therefore to examine how an integrated care intervention for community-dwelling frail elderly people affects the amount and type of formal and informal care over 12 months as compared to usual care. A quasi-experimental design with a control group was used. Data regarding formal and informal care were collected from frail elderly patients (n = 207) and informal caregivers (n = 74) with pre/post-questionnaires. Within- and between-group comparisons and multiple linear regression analyses were performed. The results showed marginal changes over time in the amount of formal and informal care in both integrated care and usual care. However, different associations between changes in formal and informal care were found in integrated and usual care. Most notably, informal caregivers provided more instrumental assistance over time if formal caregivers provided less personal care (and vice versa) in integrated care but not in usual care. These results suggest that integrated care does not necessarily change the contribution of formal or informal care, but changes the interaction between formal (personal care) and informal (instrumental) activities. Implications and recommendations for research and practice are discussed.; Trial Registration: Current Controlled Trials ISRNT05748494.