ABSTRACT: BACKGROUND:Due to a low birth rate and an aging population, Japan faces an increase in the number of elderly people without children living in single households. These elderly without a spouse and/or children encounter a lack of caregivers because most sources of care for the elderly in Japan are not provided by private agencies but by family members. However, family caregivers not only help with daily living but are also key participants in treatment decision making. The effect of family absence on treatment decision making has not been elucidated, although more elderly people will not have family members to make surrogate decisions on their behalf. OBJECTIVE:The aim is to understand the influence of family absence on treatment decision making by physicians through a cross-sectional online survey with three hypothetical vignettes of patients. METHODS:We conducted a cross-sectional online survey among Japanese physicians using three hypothetical vignettes. The first vignette was about a 65-year-old man with alcoholic liver cirrhosis and the second was about a 78-year-old woman with dementia, both of whom developed pneumonia with consciousness disturbance. The third vignette was about a 70-year-old woman with necrosis of her lower limb. Participants were randomly assigned to either of the two versions of the questionnaires-with family or without family-but methods were identical otherwise. Participants chose yes or no responses to questions about whether they would perform the presented medical procedures. RESULTS:Among 1112 physicians, 454 (40.8%) completed the survey; there were no significant differences in the baseline characteristics between groups. Significantly fewer physicians had a willingness to perform dialysis (odds ratio [OR] 0.55, 95% CI 0.34-0.80; P=.002) and artificial ventilation (OR 0.51, 95% CI 0.35-0.75; P<.001) for a patient from vignette 1 without family. In vignette 2, fewer physicians were willing to perform artificial ventilation (OR 0.59, 95% CI 0.39-0.90; P=.02). In vignette 3, significantly fewer physicians showed willingness to perform wound treatment (OR 0.51, 95% CI 0.31-0.84; P=.007), surgery (OR 0.35, 95% CI 0.22-0.57; P<.001), blood transfusion (OR 0.45, 95% CI 0.31-0.66; P<.001), vasopressor (OR 0.49, 95% CI 0.34-0.72; P<.001), dialysis (OR 0.38, 95% CI 0.24-0.59; P<.001), artificial ventilation (OR 0.25, 95% CI 0.15-0.40; P<.001), and chest compression (OR 0.29, 95% CI 0.18-0.47; P<.001) for a patient without family. CONCLUSIONS:Elderly patients may have treatments withheld because of the absence of family, highlighting the potential importance of advance care planning in the era of an aging society with a declining birth rate.