Abstract One hundred and three family caregivers of relatives with dementia were longitudinally surveyed to examine the course of caregivers' mental health after the relatives had been placed in full-time care facilities. Mental health was assessed twice, with a 6-month interval, using the Japanese version of the 60-item General Health Questionnaire. The degree of social dysfunction was significantly reduced within 6 months after placement, while the other indicators of mental health (e.g. anxiety-insomnia, depression, somatic symptom and psychiatric morbidity) were not reduced within this term. However, anxiety-insomnia and psychiatric morbidity were significantly reduced more than 6 months after placement. Analyses by caregivers' lineal relations to the relatives indicated that only daughters-in-law showed a significant decrease in anxiety-insomnia and a marginal reduction in psychiatric morbidity. This study suggests that caregivers' social dysfunction was more greatly reduced than anxiety-insomnia and psychiatric morbidity within a relatively short term after placement, and that its effects on mental health might vary with the lineal relations.