This study evaluated a joint initiative of the Social Security Administration (SSA) and the Department of Veterans Affairs (VA) to improve access to Social Security disability benefits among homeless veterans with mental illness. Social Security personnel were colocated with VA clinical staff at 4 of the VA's Health Care for Homeless Veterans (HCHV) programs. Intake assessment data were merged with SSA administrative data to determine the proportion of veterans who filed applications and who received disability awards at the 4 SSA-VA Joint Outreach Initiative sites (n = 6709) and at 34 comparison HCHV sites (n = 27 722) during the 2 years before and after implementation of the program. During the 2 years after the initiative began, higher proportions of veterans applied for disability (18.9% vs 11.1%; P < .001) and were awarded benefits (11.4% vs 7.2%, P < .001) at SSA-VA Joint Initiative sites. A colocation approach to service system integration can improve access to disability entitlements among homeless persons with mental illness. Almost twice as many veterans were eligible for this entitlement as received it through a standard outreach program.