Background: Pes anserine bursitis (PAB) is one of the most common causes of knee pain. Hence, this study aimed to compare the pain and function among all primary knee osteoarthritis (KOA) patients with or without ultrasonic‑detected PAB and the associated clinical and radiological findings. Methods: A single‑center cross‑sectional study was conducted on 245 patients with primary KOA. The more symptomatic knee examined with musculoskeletal ultrasound (MSUS), were then categorized into two groups according to the presence of PAB; PAB was graded from 0 to 2 on a semi-quantitative scale. Radiological grades of Kellgren–Lawrence were recorded. Pain and functional status was assessed by visual analog scale (VAS), Health Assessment Questionnaire‑II (HAQ‑II), and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Results: A total of 110 (44.9%) patients were diagnosed with PAB where 91 (82.7%) of them had Grade 1 and only 19 (17.3%) had Grade 2. The presence of PAB was statistically significant related (P < 0.05*) with age, VAS, HAQ‑II, WOMAC subscales, synovitis, and radiographic Grades 3 and 4. However, there was no statistically significant difference (P ≥ 0.05) between KOA patients without PAB and KOA patients with PAB, regarding sex, body mass index, Baker cyst, and effusion. Conclusion: The presence of PAB on MUS is associated with increased pain and disability in KOA. MSUS should be more widely used to establish the association between PAB and symptom severity and disability among KOA patients