Pain is common in inpatient rehabilitation patients; however, the prevalence of pain diagnoses in this population is not well-defined. This study examines comorbid pain diagnoses in inpatient rehabilitation patients across impairment groups. Adult inpatient rehabilitation patients discharged from January 2016 through December 2019 were identified in the Uniform Data System for Medical Rehabilitation® database using a literature-established framework containing ICD-10-CM pain diagnoses. Demographic data, clinical data, and pain diagnoses were compared across the 17 rehabilitation impairment groups. Of 1,925,002 patients identified, 1,347,239 (70.0%) had at least one ICD-10 pain diagnosis. Over half of all patients in each impairment group had at least one pain diagnosis. The most common pain diagnoses were limb/extremity and joint pain, with variation between impairment groups. Female sex and being in the arthritis, major multiple trauma, and pain syndrome impairment groups were associated with a greater odds of a pain diagnosis. Over half of all patients in each rehabilitation impairment group have a pain diagnosis, which varies between impairment groups. Due to the high prevalence of pain diagnoses, a new focus on pain management in inpatient rehabilitation patients is needed. Rehabilitation outcomes may also be affected by pain.