Poverty is associated with greater barriers to health care and worse health outcomes, but it remains unclear whether income support can improve health. To examine the effect of cash benefits on health care utilization and health. The City of Chelsea, Massachusetts, a low-income community near Boston, randomly assigned individuals by lottery to receive cash benefits. Participants' medical records were linked across multiple health systems. Outcomes were assessed during the intervention period from November 24, 2020, to August 31, 2021. Cash benefits via debit card of up to $400 per month for 9 months. The primary outcome was emergency department visits. Secondary outcomes included specific types of emergency department visits, outpatient use overall and by specialty, COVID-19 vaccination, and biomarkers such as cholesterol levels. Among 2880 individuals who applied for the lottery, mean age was 45.1 years and 77% were female. The 1746 participants randomized to receive the cash benefits had significantly fewer emergency department visits compared with the control group (217.1 vs 317.5 emergency department visits per 1000 persons; adjusted difference, -87.0 per 1000 persons [95% CI, -160.2 to -13.8]). This included reductions in emergency department visits related to behavioral health (-21.6 visits per 1000 persons [95% CI, -40.2 to -3.1]) and substance use (-12.8 visits per 1000 persons [95% CI, -25.0 to -0.6]) as well as those that resulted in a hospitalization (-27.3 visits per 1000 persons [95% CI, -53.6 to -1.1]). The cash benefit had no statistically significant effect on total outpatient visits (424.3 visits per 1000 persons [95% CI, -118.6 to 967.2]), visits to primary care (-90.4 visits per 1000 persons [95% CI, -308.1 to 127.2]), or outpatient behavioral health (83.5 visits per 1000 persons [95% CI, -182.9 to 349.9]). Outpatient visits to other subspecialties were higher in the cash benefit group compared with the control group (303.1 visits per 1000 persons [95% CI, 32.9 to 573.2]), particularly for individuals without a car. The cash benefit had no statistically significant effect on COVID-19 vaccination, blood pressure, body weight, glycated hemoglobin, or cholesterol level. In this randomized study, individuals who received a cash benefit had significantly fewer emergency department visits, including those related to behavioral health and substance use, fewer admissions to the hospital from the emergency department, and increased use of outpatient subspecialty care. Study results suggest that policies that seek to alleviate poverty by providing income support may have important benefits for health and access to care.