Most guidelines recommend rapid treatment initiation for patients with newly diagnosed human immunodeficiency virus type 1 (HIV-1) infection, but prospective US data are limited. The DIAMOND (NCT03227861) study using darunavir/cobicistat/emtricitabine/tenofovir alafenamide (D/C/F/TAF) 800/150/200/10 mg is a phase 3 prospective study evaluating efficacy/safety of a single-tablet regimen in a rapid-initiation model of care. Adults aged ≥18 years began D/C/F/TAF ≤14 days from diagnosis without screening/baseline results; as results became available, participants not meeting predefined safety/resistance stopping rules continued. Primary endpoint was virologic response (HIV-1 RNA <50 copies/mL; intent-to-treat; US Food and Drug Administration [FDA] snapshot) at week 48; participant satisfaction was measured via the HIV Treatment Satisfaction Questionnaire status version (HIVTSQs). Of 109 participants, 87% were male, 32% black/African American, median (range) age was 28 (range, 19-66) years, 25% of participants had HIV-1 RNA ≥100 000 copies/mL, 21% had CD4+ cell count <200 cells/µL, and 31% enrolled ≤48 hours from diagnosis. At week 48, 97 (89%) participants completed the study and 92 (84%) achieved HIV-1 RNA <50 copies/mL (FDA snapshot). There were no protocol-defined virologic failures; incidences of adverse events (AEs) and adverse drug reactions (33%) were low, no serious AEs were study drug related, and 1 (<1%) participant discontinued due to study drug related AE(s). The overall HIVTSQs score at week 48 was 58 (maximum: 60). At week 48, a high proportion of participants starting D/C/F/TAF achieved HIV-1 RNA <50 copies/mL and very few discontinued therapy. D/C/F/TAF was well tolerated, no participants discontinued due to baseline resistance stopping criteria, and high treatment satisfaction among participants was recorded. NCT03227861. © The Author(s) 2019. Published by Oxford University Press for the Infectious Diseases Society of America.