The specific heat of a large YBa2Cu3O6.92 single crystal (m≈150 mg) was measured between 0 and 27 Tesla. In contrast with previous results obtained at lower fields, the specific heat above Tc is field-dependent up to 100 K. The high magnetic fields combined with a narrow transition width (ΔTc10–90%=0.15 K in ac susceptibility) allow an accurate analysis of the different contributions in the vicinity of Tc(H=0). 2D–3D gaussian and 3D-xy critical fluctuations models are compared. A positive curvature of Hc2(T) line is observed up to 10 Tesla. The compatibility of the calorimetric and magnetic measurements [1] through Maxwell's relation is also verified.