PURPOSE: We studied the accuracy of high resolution computed tomography in staging chest wall/fissural invasion of peripheral lung cancer. MATERIALS AND METHODS: HRCT findings in 27 patients with suspected chest wall (n=18) or fissural (n=16) invasion of peripheral lung cancer were correlated with surgical and pathologic findings. The HRCT images were restrospectively evaluated for pleural thickenings adjacent to mass, maximal contact length (cm) between mass and chest wall/fissure, angle between the mass and chest wall/fissure, ratio of maximal contact to mass diameter, abnormality of extrapleural fat layer, mass extension across the fissure and fissural irregularity adjacent to mass. Various CT findings and the presence or absence of chest pain were correlated with surgical and pathologic findings. RESULTS: For the evaluation of chest wall invasion, abnormality of extraphleural fat layer was the most useful finding (sensitivity 100 %, specificity 36 %, accuracy 61 %). The remaining HRCT findings proved to have high sensitivity but low specificity, and a high false positive rate. For chest pain, sensitivity was 43 % and specificity, 82 %. In cases without chest pain, the positive predictive value of extraphleural fat abnormality was 44 % ; in the absence of chest pain and extrapleural fat abnormality,positive predictive value was zero. The evaluation of transfissural tumor invasion using variable HRCT findings proved to be accurate, especially when the criteria of mass extension across the fissure and fissural irregularity adjacent to the mass were used (accuracy 81 % and 75 %, respectively). CONCLUSION: Using the finding of 'extrapleural fat abnormeality', HRCT was accurate in the staging of chest wall invasion and its predictability was betten than that of other results obtained with conventional CT. Chest pain had high specificity but low prevalence, and extrapleural fat abnormality was more valuable in cases without chest pain. HRCT proved to be accurate in the evaluation of transfissural invasion of lung cancer using the findings 'fissural cross' and 'fissural irregularity'.