Objective To identify prognostic factors for the effectiveness of needle aspiration of calcific deposits (NACD) for rotator cuff calcific tendinitis (RCCT) Methods One hundred forty-nine patients with symptomatic RCCT were included in a prospective cohort study. Pain (VAS), shoulder function (SST and DASH), and quality of life (EQ-5D) were assessed at baseline and at 3, 6, and 12 months post-NACD. Univariate analyses (independent t tests or Mann-Whitney U tests depending on the distribution of data) were performed to build a multivariable linear regression model. Stepwise regression analysis through backward elimination was performed to evaluate the effect of predefined prognostic factors on the outcome. Results Patients who underwent multiple NACD procedures had less reduction of pain (p < 0.01). Furthermore, a larger reduction in VAS pain scores at 3 months post-NACD was associated with a larger reduction in VAS pain scores at 12 months (p < 0.01). More improvement of SST and DASH scores at 3 months was associated with better SST, DASH, and EQ-5D scores at 12 months (p < 0.01). Smaller-size calcific deposits were associated with less improvement of DASH (p = 0.03) and EQ-5D scores (p = 0.01). A longer duration of symptoms prior to NACD was associated with less improvement of EQ-5D scores (p = 0.01). Conclusions A good initial response after NACD is associated with better outcomes at 12 months. Patients with a longer duration of symptoms prior to NACD and patients who require multiple procedures showed inferior outcomes in terms of pain reduction and improvement of quality of life. Smaller-size calcific deposits are associated with a less favorable outcome of shoulder function and quality of life scores and might therefore be less susceptible for NACD. Key Points • A good initial response to NACD is associated with a better outcome in the longer term. • A longer duration of symptoms and the need for multiple NACD procedures are associated with inferior outcomes. • Smaller-size calcific deposits seem less susceptible for NACD.