Abstract: Background and purpose: The use of Compton cameras for imaging radioisotopes in nuclear medicine offers potential advantages over conventional gamma cameras in some aspects. In this work, we present the first results in this field with the Compton camera prototype MACACO III after a measurement campaign in La Fe Hospital (Valencia, Spain). Methods: Images of Derenzo-like phantoms filled with 18F-FDG and 131I-NaI have been obtained with MACACO III and, in the latter case, with gamma cameras available in the hospital. Subsequently, a metastatic lesion in a patient treated with 131I-NaI after thyroid gland resection was imaged. Results: The 18F-FDG phantom images show the prototype capability of identifying up to 4 mm diameter rods. The measurements with 131I-NaI-filled phantoms demonstrate the clear improvement of the spatial resolution attainable with MACACO III when compared with images obtained with the gamma cameras available in the hospital. Finally, the image of the patient metastatic lesion obtained with the Compton camera was found to be consistent with the gamma camera inspection image. Conclusion: These encouraging results demonstrate MACACO III's capability for radiopharmaceutical imaging and open a door for its application to nuclear medicine.