Objectives: The socioeconomically disadvantaged oldest old (people aged 85 years and over) are more vulnerable to social exclusion than the general population. Using a population representative sample, this paper examined associations between sociodemographic characteristics and social exclusion among the oldest old. Methods: This cross-sectional study included 307 participants aged 85 years and over from the Household, Income and Labour Dynamics in Australia (HILDA) Survey. Sociodemographic characteristics were measured using household composition, country of birth, housing tenure, income, education and neighbourhood-level disadvantage. Three social exclusion domains were derived representing unsupportive relationships, neighbourhood exclusion and community disengagement. Analysis was undertaken separately for men and women. Results: Among men, living alone was associated with higher levels of unsupportive relationships (β = 11.6, 95%CI 2.1, 21.0) and having a lower income was associated with lower levels of neighbourhood disunity (β = −16.7, 95%CI −31.2, −2.2). Among women, living alone was associated with lower levels of community disengagement (β = −7.2, 95%CI −13.4, −0.9) and neighbourhood disadvantage was associated with lower levels of neighbourhood disunity (β = −10.4, 95%CI −19.6, −1.2). Both men and women with lower levels of education had higher levels of community disengagement (men: β = 8.3, 95%CI 1.9, 14.7; women: β = 17.0, 95%CI 8.6, 25.5). Conclusions: This study showed few and unexpected associations between sociodemographic characteristics and social exclusion among oldest-old Australians, suggesting a homogeneous effect of advancing age. Government approaches aimed at reducing social exclusion in this age group should consider gender and taking action across all socioeconomic stratification. Further research is warranted to understand the underlying mechanisms linking sociodemographic characteristics to social exclusion.