Background and Objective: Patients with idiopathic scoliosis often have hypokyphosis in their spines, but some patients may exhibit an increase in kyphosis instead. The aim of this study was to define the effect of the kyphosis on the flexibility of scoliotic curves. Materials and Methods: A total of 100 cases of idiopathic scoliosis were studied with standing posteroanterior and lateral radiographies of the entire spine. Based on the degree of kyphosis, cases were classified into two groups and compared statistically. Results: Group 1 included 61 cases with less than 50 degrees of kyphosis, and group 2 included 39 cases with equal or more than 50 degrees of kyphosis. The average of scoliosis in group 1 was 57.5 degrees compared with 51.3 degrees in group 2, and the averages of the flexibility index were 57.1 vs. 52.7, respectively. The two groups were also compared according to the standing and supine bending scoliosis, flexibility index, and the correlation between kyphosis and flexibility index. There was neither a significant correlation between the kyphosis and scoliosis curves (P>0.05 r<0.5) nor in the flexibility of scoliosis curves between the two groups (P=0.23). Conclusion: In our study, the presence of kyphosis seems to have no impact on scoliosis curves in patients with idiopathic scoliosis.