Background Rib fractures are common injuries among traumatically injured patients, and elderly patients with rib fractures are at increased risk for adverse events and death. The purpose of this study was to determine if oral Per os (PO) acetaminophen is as effective as intravenous (IV) acetaminophen in treating the pain associated with rib fractures. Methods We performed a single-center, randomized, placebo-controlled, double-blinded study. Trauma patients who were ≥65 years old and had ≥1 rib fracture were included in this study. Patients were randomized into IV acetaminophen and oral placebo (n = 63) or IV placebo and oral solution acetaminophen (n = 75) groups. The primary outcome was a mean reduction in pain score at 24 hours, and secondary outcomes included opioid use, intensive care unit (ICU) length of stay (LOS), hospital LOS, hospital mortality, the difference in incentive spirometry, and development of pneumonia. Results Among the 138 patients included, there was no statistically significant difference between the 2 study groups in a mean reduction in pain score at 24 hours after injury (PO: 3.24, IV: 2.49; P = .230). Opioid pain medication use was equivalent between groups ( P = .212), and there was no significant difference in hospital mortality rate between groups ( P = .827). There was no statistically significant difference in ICU LOS, hospital LOS, or development of pneumonia. Discussion In elderly trauma patients (age ≥65 years) with 1 or more rib fractures, PO acetaminophen is equivalent to IV acetaminophen for pain control, with no difference in morbidity or mortality. Oral acetaminophen should be preferentially used over IV acetaminophen when treating the elderly trauma patient with rib fractures.