It is uncommon for patients to present with bone metastases while the primary tumor is still unknown. The case of a patient with bone metastases as primary presentation of leiomyosarcoma, who was diagnosed after a 18F-FDG PET-CT and a CT-guided biopsy of the adrenal gland is described. If after routine physical, laboratory and radiological investigations no diagnosis can be made, 18F-FDG PET should be added to the conventional work-up of patients with unknown primary cancer. In this way, unnecessary and enduring suffering of symptomatic patients may be prevented.