PURPOSE: Patients with metastatic colorectal cancer (mCRC) undergoing systemic treatment often experience toxicities. Although exercise may improve physical fitness and quality of life and counteract treatment toxicity, knowledge in patients with mCRC is limited. The ongoing randomized controlled AMICO trial evaluates the effects of supervised exercise on clinical outcomes. The present qualitative study was a pre-planned part of this trial aiming to capture adherence, satisfaction, and perceived effects of exercise among patients with mCRC. METHODS: Patients with mCRC receiving first-line systemic treatment were randomized (1:1:1) to a control group or one of two supervised exercise arms including continuous aerobic exercise with either resistance exercises or high-intensity interval training. Semi-structured interviews with patients in the exercise arms were transcribed verbatim and thematically analyzed. Descriptive data on adherence (exercise logs) and satisfaction (questionnaire) was collected to complement and contextualize the qualitative findings. RESULTS: Twenty-one patients were interviewed. Median exercise attendance was 67% [IQR 35-91], and the median satisfaction score was 8 [IQR 8-9] out of 10. Patients valued the guidance and knowledge of the physical therapist and expressed interindividual preferences regarding training content. Patients experienced that exercise improved their physical and mental wellbeing and helped them to endure treatment. Perceived exercise barriers were treatment toxicity, physical problems, and hospital appointments. Perceived exercise facilitators included adequate tailoring and internal or external motivation. CONCLUSION: Patients with mCRC appreciated exercise during systemic treatment and perceived several beneficial effects, both physically and mentally. Exercise attendance varied and barriers were mainly treatment- and disease-related. TRIAL REGISTRATION: Clinical trial. GOV ID: NCT04754672. Date of registration: 04-12-2020.