BACKGROUND: Rapid linkage to HIV care and antiretroviral therapy (ART) initiation is now the standard of care for treating people with HIV (PWH). Understanding and intervening on barriers to rapid enrollment and ART initiation are needed to meet the goals of the Ending the HIV Epidemic in the U.S. initiative. METHODS: We analyzed 2021 data from the Medical Monitoring Project on characteristics of 455 facilities providing care to a national probability sample of U.S. PWH. RESULTS: Overall, only 19.9% (95% CI 16.0%-23.9%) of HIV facilities could routinely offer a first appointment in <1 business day (rapid enrollment). The most commonly reported barriers to rapid enrollment were insufficient provider capacity (56%), patient preference (50%), and patients lacking required documents (19%). The most commonly reported documents required for enrollment were positive HIV antibody or detectable viral load (52%), government-issued identification (36%), proof of residence (24%), and proof of income (22%). RWHAP-funded facilities more frequently required these documents than non-RWHAP-funded facilities. Most facilities (73%) were routinely able to obtain a 30-day supply of ART during the first HIV care provider visit (rapid ART initiation). The most commonly reported barriers to rapid ART included unavailable test results (56%), delays in getting medication paid for (49%), unavailable starter packs (36%), inability to afford copayment (31%), and patient preference (29%). CONCLUSION: Structural, provider-related, or patient-level barriers may delay rapid clinic enrollment or ART initiation. HIV care programs can benefit from removing barriers to care, easing requirements for clinical enrollment and ART prescriptions, and improving patient readiness.