Antiretroviral postexposure prophylaxis (PEP) may be underutilized in sexual assault cases in Kenya. This study evaluated the characteristics of survivors of sexual violence attending the Gender-Based Violence Recovery Center (GBVRC) at the Kenyatta National Hospital and reviewed the uptake, adherence, and outcomes of those initiated on PEP. In a retrospective cohort, data from charts of the assaulted seen at the GBVRC from 2009 to 2012 were abstracted. Data were collected describing sociodemographic characteristics, nature of sexual assault, HIV serostatus, and aspects of the PEP care cascade. Characteristics of participants who received PEP were compared with those who did not receive PEP. We enrolled 385 assaulted persons; 331 (86%) were female; the median age of the assaulted persons was 21 (interquartile range 14–28) years; and 61 (15.8%) were children aged 10 years and younger. Of 379 assaults with descriptions, 330 (85.7%) were vaginal assaults and 40 (10.3%) were penile-anal assaults. Most perpetrators were unknown to the assaulted 220 of 384 (57.3%). All assaulted persons were offered HIV testing and 359 (93%) accepted testing; 346 (96.4%) of 359 assaulted persons tested HIV negative. In total, 207 (53.8%) of 385 sexual assault survivors initiated PEP. Only 70 (34%) completed 28 days of PEP, and only 21 (10.1%) returned for repeat HIV test at 3 months. In conclusion, PEP was only initiated in 54% of sexual assault cases. The care cascade showed that late presentation and poor adherence were the greatest gaps in PEP provision. Earlier presentation for PEP should be promoted among sexual assault in areas of high HIV prevalence.