Aim To evaluate grading of thumb carpometacarpal joint (CMCJ) osteoarthritis (OA) using ultrasound, correlating findings with disability and treatment response. Materials and methods Patients with symptomatic thumb OA attending for ultrasound-guided CMCJ steroid injection and a group of asymptomatic controls were recruited prospectively. Thumb CMCJ ultrasound was graded (osteophytes, joint-space narrowing, capsule size, and measured capsule size), and a Disabilities of the Arm Shoulder and Hand (DASH) questionnaire was completed for each patient. Symptomatic patients then underwent injection with DASH repeated 6 weeks post-treatment. Ultrasound features were correlated with the initial DASH disability score and response as defined by change in DASH 6 weeks after treatment. Results Thirty-one patients with symptomatic OA and 37 asymptomatic controls were recruited. With the exception of osteophytes (p = 0.017), no statistically significant correlation was demonstrated between severity of ultrasound features and patient disability. However, all features demonstrated statistically significant higher grades in the symptomatic group compared to controls. Ultrasound grading did not have statistical correlation with treatment response. Conclusion No correlation was found between the majority of ultrasound features and the clinical severity of OA or likely response to treatment. However, these features are significantly more common in the symptomatic population.