HIV self-testing (HIVST) is recommended by the World Health Organization, but implementation remains limited. This cross-sectional study evaluated HIVST uptake among female entertainment workers (EWs), men who have sex with men (MSM), and transgender women in Phnom Penh, Cambodia, to inform national implementation. Between December 2018 and September 2019, individuals reached through community outreach or via online advertising were offered HIVST or referrals to facility-based testing. Participants opting for HIVST could choose between test kits employing oral-fluid or finger-prick-based sample collection; and between an "assisted" option in which outreach staff offered instructions and assistance and an "unassisted" option in which participants received a kit with instructions for use. A structured questionnaire was administered to facilitate descriptive statistics and tests for associations between participant characteristics and HIV testing preferences and outcomes. Among 1,241 eligible individuals; 1,210 (97.5%) provided responses for analysis. Of these, 1,203 (99.4%) were recruited through outreach; 7 (0.6%) through online advertising. Among those recruited by outreach, 1,186 (98.6%) opted for assisted HIVST, and 1,065 (88.5%) opted for oral-fluid versus finger-prick testing. All individuals recruited through online advertisements opted for unassisted oral-fluid testing. Among all participants, 455 (37.6%) were MSM, 325 (26.9%) were transgender women, 430 (35.5%) were female EWs, and overall, 71.7% reported never previously testing for HIV. A total of 84 participants (6.9%) received reactive screening results and 81 (97.5%) were linked to treatment. Uptake of HIVST was high, and most participants preferred oral-fluid over finger-prick-based testing. Many individuals (72%) who had never previously accessed HIV testing services participated in HIVST, with high rates of reactivity.