Purpose To determine the main reasons why patients with trapeziometacarpal osteoarthritis (TMC OA) seek treatment, their pretreatment expectations for the final outcome, fulfillment after one year, and predictors of fulfillment of the expectation. Methods We included 163 patients with TMC OA. They filled out questionnaires assessing expectations and functional status before and at 3, 6, and 12 months after treatment. Results Pain reduction was the most important reason why 65% of all patients sought treatment, whereas 17% and 13% requested treatment to improve hand function and activities of daily living, respectively. No patients considered improved appearance of the hand to be the main reason for undertaking treatment. Expectations before treatment were anticipated to be totally or mostly fulfilled by 93% of surgically treated patients and 59% of patients treated with corticosteroid injection. After one year, 77% of surgically treated patients rated their expectations as completely or mostly fulfilled, compared with 24% of patients treated with corticosteroid injections. Including all variables before treatment in a best-fit regression model, fulfillment of patients' expectations could not be sufficiently predicted. However, with addition to the model of the outcome of pain at one year, 48% of the variance of fulfilled expectations could be accounted for. Conclusions Patients with TMC OA predominantly visit hand surgeons seeking treatment to reduce pain, whereas function and aesthetics have minor roles. Based on variables before treatment, no prediction can be made regarding whether expectations will be fulfilled after treatment because residual pain at one year contributes considerably to the variance in fulfilled expectations. Clinicians should assess patients' expectations before treatment and explain realistic treatment outcomes to obtain best treatment results. Type of study/level of evidence Therapeutic II.