BACKGROUND In view of the increasing integration of health and social care, there is an urgent need to know how health service day hospitals and social service day centres are being used, and by whom. OBJECTIVE We aimed to compare users of day hospitals and centres in terms of their social networks, needs for care and demographics. METHODS A cross-sectional, comparative study of service users at two day hospitals and four day centres compared their social networks, needs and characteristics. RESULTS Day centre clients had much larger social networks, including a three-fold difference in total contacts and two-fold difference in confidants, but had more needs for care, particularly relating to psychological distress. They were also older on average than day hospital patients and were a more long-term group. CONCLUSIONS It is vital to understand differences between health service day hospitals and social service day centres given the increasing integration of health and social care. The present study shows that the two user groups are significantly different. It is unlikely that the needs of most day care users could be met by either service interchangeably.