We compared overall survival for metastatic breast cancer (MBC) patients monitored with CE-CT, FDG-PET/CT or a combination of them in an observational setting. Patients with biopsy-verified (recurrent or de novo) MBC (n = 300) who were treated at Odense university hospital (Denmark) and response monitored with FDG-PET/CT (n = 83), CE-CT (n = 144), or a combination of these (n = 73) were followed until 2019. Survival was compared between the scan groups, and were adjusted for clinico-histopathological variables representing potential confounders in a Cox proportional-hazard regression model. The study groups were mostly comparable regarding baseline characteristics, but liver metastases were reported more frequently in CE-CT group (38.9%) than in FDG-PET/CT group (19.3%) and combined group (24.7%). Median survival was 30.0 months for CE-CT group, 44.3 months for FDG-PET/CT group and 54.0 months for Combined group. Five-year survival rates were significantly higher for FDG-PET/CT group (41.9%) and combined group (43.3%), than for CE-CT group (15.8%). Using the CE-CT group as reference, the hazard ratio was 0.44 (95% CI: 0.29-0.68, P = 0.001) for the FDG-PET/CT group after adjusting for baseline characteristics. FDG-PET/CT detected the first progression 4.7 months earlier than CE-CT, leading to earlier treatment change. In this single-center, observational study, patients with metastatic breast cancer who were response monitored with FDG-PET/CT alone or in combination with CE-CT had longer overall survival than patients monitored with CE-CT alone. Confirmation of these findings by further, preferably randomised clinical trials is warranted.