Little is known about whether social factors are related to readmissions among non-elderly adults admitted to safety-net hospitals (SNHs), particularly after health reform that lowered barriers to obtaining post-discharge medical care through insurance expansion. We conducted a prospective cohort study of 713 non-elderly adults at two of Massachusetts' largest SNHs eight years after Massachusetts' health reforms. Social factors were assessed through in-person interviews and electronic health record data. After adjustment for clinical variables, public insurance, White race/ethnicity, being unemployed, being unstably housed, having an alcohol-related index admission, and having a substance use-related index admission remained associated with readmissions at 90 days. At 30 days, public insurance, worry about safety or condition of housing, and having an alcohol-related index admission remained associated with readmissions. Unadjusted models were consistent with these findings. Accounting for social factors in readmission adjustment schemes used by payers may be important for ensuring payment equity.