Critical access hospitals are important providers of care for rural and other underserved communities, but they face staffing and quality challenges while operating with low margins. Medicaid expansion has been found to improve hospital finances broadly and therefore may have permitted sustained investments in staffing and quality improvement at these vulnerable hospitals. In this difference-in-differences analysis, we found that critical access hospitals in Medicaid expansion states did not have statistically significant postexpansion increases in operating margins relative to hospitals in nonexpansion states. Nor did we see evidence of statistically significant differential improvement at critical access hospitals in expansion versus nonexpansion states on either staffing measures (physicians and registered nurses per 1,000 patient days) or quality measures (percentage-point changes in readmissions and mortality within thirty days of admission for pneumonia or heart failure). These findings suggest that critical access hospitals may need to take additional measures to bolster finances to provide continued support for the delivery of high-quality care to rural and other underserved communities.