Objective To test the possibility that the thoracic defomity is a risk factor of the diopathic pneumothorax in youth by making a statistical analysis of the thoracic sagittal diameter and transverse diameter ratio in patients and normal people. To study the correlation between this ratio and age of the patients. Methods 107 cases of idiopathic pneumothorax were taken as subjects and other 105 cases in' the same period with normal pneumothorax were used as the control group. T-test,correlation study and scottered spot maps were made based on the ratio of vertical and horizontal diameters,the mean and the age. Results The mean thorax aspect ration( MTAR) of the patients with spontaneous pneumothorax was 0.38, and MTAR in normal people was 0.44, indicating a statistical significance ( P < 0.01) of the difference of MTAR between the two groups. The age of the patients' first onset age and the ratio of vertical and horizontal diameter was positively correlated. Conclusion Thoracic deformity of idiopathic pneumothorax had a higher incidence in young people,and there was a positive correlation between of the age of their first onset and the ratio of vertical and horizontal tracks.