Both light-scattering and differential scanning calorimetry (DSC) measurements account for the existence of a dramatic thermal hysteresis effect occurring in micellar solutions of gangliosides. Light-scattering measurements reveal that the mean aggregation number of ganglioside micelles assumes different values depending on the sample thermal history, a hysteresis phenomenon that completely disappears above a well-defined temperature. On the other side, DSC measurements assess that the heat-capacity variation versus temperature for the ganglioside micellar system depends as well on the thermal history of the sample. Although rather complicated, the calorigrams show a peak associated with the melting of the micelle hydrophobic core. The position of the peak undergoes changes consistent with the observed hysteresis of the mean aggregation number. The two parallel descriptions, geometric and calorimetric, can be clearly correlated as two aspects of the same phenomenon and give support to each other. The hysteresis behavior below a critical temperature is related to cooperative conformational variations of the oligosaccharide headgroup at the micellar surface. Such surface phenomena are coupled to the well-known order-disorder transition of the hydrophobic chains in the core via the geometric constraints imposed by the confinement of the amphiphiles in the micellar aggregate.