Metastasectomy after the primary surgical treatment of colorectal cancer may prolong survival in patients with resectable recurrences. Dedicated 18F-FDG-PET is of growing interest as a diagnostic tool in the staging and diagnosis of recurrent disease. We wanted in our departments to investigate whether a dual-head gamma camera with coincidence detection could serve as a substitute for the dedicated PET scanner. Twenty consecutive PET scans of 18F-FDG were performed by means of an Adac VertexPLUS gamma camera in 14 patients with colorectal cancer and four patients with anal cancer with known or suspected recurrences. Evaluation of the patients were, however, according to the routine in the department. In fourteen patients one or more abnormal foci were detected by PET, nine of these were verified by biopsy and one by renewed CT scan. In the four patients with negative PET the findings were in agreement with later biopsies. In one patient PET was "falsely" negative with regards to other processes than a solitary metastasis to be removed, as he six months later revealed dissemination confirmed by biopsy. Four patients with positive PET findings and elevated CEA remain to be evaluated. We conclude that PET with a coincidence detection gamma camera in this preliminary study seems to have the same possibilities to stage and diagnose recurrent anal- and colorectal cancer as the dedicated PET scanner.