Gastrointestinal stromal tumors (GIST) are the most frequent mesenchymal tumors of the gastrointestinal tract. They are generally located in the stomach or the small bowel and the potential for becoming malignant varies. Due to their expression of c-kit protein, a positive diagnosis as well as a specific targeted treatment by molecular biology (imatinib) are available. Computed tomography is the best imaging method for diagnosis, staging and follow-up of GIST. They appear as a well-defined exophytic mass with heterogeneous enhancement after intravenous injection of iodinated contrast material. They may contain areas of necrosis and/or haemorrhage and enlarged lymph nodes are exceedingly rare. Most common metastatic sites are the liver and mesentery. Large tumour size and liver or mesenteric metastases are computed tomography criteria for a high malignant potential. After treatment, decrease in tumour size, number and density of lesions and the disappearance of enhancing nodules suggest a positive response to imatinib therapy, whereas a new enhancing nodule within a mass is the usual pattern of recurrence. Positron emission tomography may be useful in specific cases when clinical data are inconsistent with computed tomography criteria.