Abstract: Colorectal cancer is one of the most common kinds of carcinoma in China and the morbidity has been increasing continually.Although much effect has been made in the field of treatment of colorectal cancer,the progress is not significant.So the prompt and accurate preoperative diagnosis,staging and restaging are very important clinical concerns for individual treatment;¹⁸F-FDG PET/CT,which combines the anatomical and functional imaging information,has been widely applied in these aspects and showed significantly clinical value.Most lesions of colorectal carcinoma demonstrate highly increased FDG uptake.The diagnostic accuracy of ¹⁸F-FDG PET/CT for primary lesions commonly ranges from 92.7%~95.0%,with a high sensitivity and specificity.¹⁸F-FDG PET/CT can earlier detect metastasis and is considered the best method of choice for preoperative staging.The diagnostic sensitivity,specificity and accuracy for the recurrence and metastasis ranges from 89%~94.6%,83.3%~100%,90%~98.3%,respectively.Comparing with the conventional imaging modalities,¹⁸F-FDG PET/CT can found more small and occult recurrent and metastatic lesions.Additionally,the metabolic changes of lesions can be earlier detected by ¹⁸F-FDG PET/CT than by other methods such as CT,MRI,and ultrasonography,which are based on morphological characteristics.Therefore,¹⁸F-FDG PET/CT can play an important role in the evaluation of therapeutic effects and can provide evidence for further clinical decisions.In short,PET/CT is a safe,noninvasive functional imaging method of diagnosis,staging and restaging for colorectal carcinoma.