To assess the effects of platelet-rich plasma (PRP) injection among patients with thumb carpometacarpal (CMC) joint osteoarthritis (OA). Retrospective chart review with follow-up questionnaires/surveys. Post-procedure, patients were sent standardized, automatically-generated follow-up questionnaires, and contacted for a survey regarding patient-reported outcomes. Single institution (tertiary care hospital) outpatient clinic from 2015 to 2020. Nineteen adult patients (9 women; average age 65.0 [±6.3 years]) who received a PRP injection for OA of 1 or both thumb CMCs (N=19). Platelet-rich plasma injection. Outcome measures included symptom improvement (subjective, visual analog scale), duration of benefit, subsequent procedures, satisfaction, and side effects/adverse events. Cellular composition of whole blood and PRP injectate (platelets, erythrocytes, leukocytes, neutrophils, lymphocytes, and monocytes) were analyzed. Subjects reported moderate or excellent symptom improvement in 68.8% of injected joints and were moderately or very satisfied with 68.8% of the procedures. Mean patient-reported duration of benefit was 15.6 months (±19.5) months (mean duration of follow-up: 32.4 [±18.1] months). There were no major complications attributed to the procedures, but 1 patient was diagnosed with presumed unrelated lymphoma 2 weeks post-procedure. PRP mean platelet concentration was 1787.77 (±687.14) × 109/L, resulting in a mean platelet concentration factor of 8.80 (±4.19) times baseline and mean platelet dose of 1881 × 106. Other PRP cell concentration factors were erythrocytes, 0.02; neutrophils, 0.14; lymphocytes, 3.76; and monocytes, 3.29. PRP injection appears to be a safe and potentially effective treatment option for pain related to first CMC OA. Further study is needed to optimize treatment protocols and better understand which patients are most likely to benefit.