The thermal and structural behavior of the complex beta-cyclodextrin 1,7-dioxaspiro[5,5]undecane.9H(2)O is studied between 23 and 150 degreesC using the coupling of differential scanning calorimetry (DSC) and time-resolved X-ray diffraction as a function of temperature (XRDT). A drastic structural change between the low-temperature (LT) and the high-temperature (HT) phases, correlated with an endothermic DSC peak, shows that a solid-state phase transition takes place at about 110 degreesC on heating. A model for the HT phase is built from the knowledge of the LT phase crystal structure and is ascertained by simulated X-ray diffraction patterns. Both LT and HT structures are columnar, and the phase transition is explained by the loss of water molecules located between the beta-cyclodextrin channels, leading to their close contact. The HT phase is a new structural form of the beta-cyclodextrin complex that is fully dehydrated. The recordings of both DSC and XRDT from the same sample employed for the first time to the study of cyclodextrin phase transition allowed an unambiguous splitting of the thermal and structural evolutions and was revealed to be a very efficient tool for the monitoring of kinetically controlled processes.