Fall prevention strategies exist, but little is known about factors that influence whether they are used. We assessed whether social isolation modifies the association between fear of falling (FOF) and bathroom environmental modification. Data were included from 2858 Medicare beneficiaries in the National Health and Aging Trends Study. FOF and social isolation were assessed at baseline (2011); new bathroom modifications were assessed 1-year post-baseline. Social network size was dichotomized as any versus no social contacts. Logistic regression assessed associations between FOF and bathroom modification. Effect modification between FOF and social isolation was assessed with multiplicative interaction terms. FOF was associated with increased odds of bathroom modification. We observed a statistically significant interaction between FOF and social isolation ( = 0.03). Among those with no social contacts, FOF was associated with reduced odds bathroom modification that did not reach statistical significance (OR 0.5, 95% CI 0.2-1.3).