I will present new results on the structure of molecular cloud in which we identify in massive star forming regions, such as Cygnus-X, characteristic scales of the order of ~1 pc. Such scales are absent in low mass, turbulence dominated clouds. Going to larger scales, I will show that characteristic scales also exist in the large scale ISM traced by the HI gas distribution. These results will be compared to those coming from the analysis of high-resolution simulations of entire galactic disks.