We discuss the determination of the expansion of the Orion association. Previous estimates of expansion in associations have employed simplified linear approximations which only required the observation of proper motions (cf. Lesh, J.R., ApJ, 152, 905, 1968). We have used proper motions obtained by Smart (PhD Thesis, Univ. of Florida, 1993) with previously obtained membership criteria to investigate this hypothesised expansion without conclusive results.