The causative factors of shoulder dislocation are variable and complex. Among these factors. the author studied retrospectively the significance of G/H ratio in three groups; recurrent dislocation traumatic dislocation and normal contrast group. The results were as follows: 1. The mean value of G/H ratio was 74.1$pm$4.7% in 59 cases of recurrent dislocation 75.9$pm$3.2% in 11 cases of traumatic dislocation and 78.2$pm$4.6% in 148 cases of control group. 2. There was no significant difference in G/H ratio between recurrent dislocation and traumatic dislocation (P>0.05) 3. There was significant difference in G/H ratio between traumatic dislocation and control group. (P<0.01) 4. There was significant difference in G/H ratio between traumatic dislocation and control group.(P<0.05) Therefore small glenoid compared with humeral head (low G/H ratio) was meaningful as one of causative factors in shoulder dislocation.