Background: Parkinson's disease (PD) is often associated with depression and anxiety. The availability of evidence-based psychological interventions is low. Objective: This pilot study investigates the feasibility and preliminary effect of internet-based cognitive behavioral therapy (ICBT) for depression and anxiety in PD. Methods: 9 patients with PD with comorbid symptoms on the relevant subscale of Hospital Anxiety and Depression Scale (HADS), of either depression (HADS-D N 7) or anxiety (HADS-A N 7) received 12 weeks of ICBT, specially adapted for depression and anxiety in PD. Primary outcome was change in depression and anxiety symptoms, measured with HADS total score. Effects on non-motor symptoms, PD specific health and quality of life and insomnia were explored, plus the participant's involvement, satisfaction, and subjective evaluation of the treatment. Results: Participants reported lower symptoms on HADS after ICBT (Cohen's d = 0.79, p b 0.05). However, levels of inactivity were rather high and questionnaires and comments from participants suggested that the treatment can be improved, for example by adding more therapist support. Conclusions: The results suggest that ICBT could be a feasible way to alleviate depression and anxiety in PD. However, a somewhat simplified treatment and different ways to provide support to enhance adherence and outcome are warranted.