The transonic flowfield about a secant-ogive cylinder boattail with a turbulent boundary layer has been studied. A joint theoretical and experimental effort is presented which compares the results of a generalized axisymmetric Navier-Stokes code, a composite inviscid boundary-layer/shock interaction solution method, and experiment. The experimental longitudinal pressure distribution at A/=0.94 and 0.97 at a = 0 deg are generally well predicted by both theoretical techniques although the Navier-Stokes solutions are shown to be superior in describing the details, such as upstream effects of expansion corners and the position and magnitude of minimum pressure regions. Both theoretical solutions predict the boundary-layer velocity profiles very well in all cases with the largest differences occurring just downstream of the boattail corner. Comparisons of displacement thickness and skin friction distributions are also presented.