OBJECTIVE: The objective of this study was to explore the time spent and cost on caring by families of persons with Alzheimer in Spain. METHODS: Questionnaires were answered by 86 carers, caring for persons with Alzheimer disease. Questions were focused on time spent on caring: activities in daily living (ADL), instrumental ADL (IADL), Social/recreational and Behaviour management. The opportunity and replacement costs approaches of informal care that occurred in 2001 in Spain were also estimated. Disease stage was determined using the Clinical Dementia Rating (CDR) scale. RESULTS: Informal care, measured as hours spent caring, was about 293 hours per month for primary and secondary caregivers. Approximately 32, 46, 9 and 16% of the total time of informal support in ADL, IADL, Social/recreation and Behaviour respectively. Informal care hours for mild, moderate and severe Alzheimer patients were 196, 268 and 416 hours per month respectively. From the opportunity cost approach the annual cost for caregivers for severe, moderate and mild patients were 16,274, 10,484 and 7,668 euros respectively. For the replacement approach the costs for severe, moderate and mild patients were 25,333, 16,631, and 9,932 euros respectively. Informal support and costs, in terms of ADL, IADL, Social/recreation and Behaviour increased with Alzheimer severity. CONCLUSIONS: This study gives some new perspectives on informal care giving for persons with Alzheimer. Informal care for Alzheimer represent a significant hidden cost to Spanish society. This aspect of caring must be addressed by the development of well-targeted respite and relief support programmes. Because the Spanish community is rapidly aging, this informal care burden may increase significantly in the future.