Older adults in need of long-term care often receive help from both informal and formal caregivers. The division of tasks between these different types of caregivers may vary among such mixed care networks. Traditional models of task division suggest that formal and informal caregivers may either supplement each other or specialise in the care activities performed. Our study explores the determinants of various forms of task division in the Netherlands, using data collected in 2007 on 458 mixed care situations. Four types of task divisions of informal and formal care are distinguished: the complementation model [neither Activities of Daily Living (ADL) nor instrumental ADL (IADL) tasks shared, 14%], the supplementation model (both ADL and IADL tasks shared, 39%) and informal and formal specialisation (one type of task shared, one type of task not shared, 27% and 20% respectively). Marginal effects calculated with multinomial regression analyses show that the intensity of care provision, the informal caregivers' motives and the presence of privately paid help - more than care receiver's health - are related to type of task division with formal care. For example, when the informal caregiver provides more hours of help and out of a strong personal bond, the likelihood of informal specialisation increases, whereas the likelihood of formal specialisation decreases. When privately paid help is present, the complementation model is more likely, whereas the supplementation model is less likely to be found. Results are discussed regarding the differential consequences for co-ordination and co-operation in mixed care networks. © 2013 John Wiley & Sons Ltd.