The SYLMET Trial is a randomized trial to compare simultaneous and two-staged resection of primary colorectal and synchronous liver metastases. This is an investigator-initiated, multicentre, randomized controlled trial to assess complications (primary endpoint), survival, cost-effectiveness, and quality of life (secondary endpoints).This trial will include patients with resectable primary tumour in the colon or upper rectum with less than five liver metastases that is possible to treat with surgical resection and/or ablation (RFA/MWA) at time of evaluation.