In a randomized controlled study, positive effects were found of a support program for caregivers of dementia patients. The aim of this study is to identify in a secondary analysis the prognostic factors of success of the support program by comparing characteristics of patients and primary caregivers for whom the support program was effective with those for whom the program was not effective (n = 49 pairs of patients and caregivers). The theoretically based individualized support program which is presented in this article, was most effective with regard to primary caregivers' sense of competence for females sharing a household with the dementia patient. The program was most effective in reducing the number of patient admissions when patients did not receive support from a district nurse and the primary caregivers experienced less emotional support from the informal network. A proactive approach by offering this flexible support before caregivers ask for support may prolong the stage in which they feel able to care for patients at home. Offering this support to females, who usually are supposed to care for the patient without assistance, may be both effective and efficient.