Abstract: A fluctuating volume adjustable prosthetic socket for below-the-knee amputees comprising a generally hollow main body support of rigid plastic; a posterior popliteal section of rigid plastic generally contoured to conform to the posterior anatomy of the knees; elasticized sleeve means supported at lower portions of said posterior popliteal section; and cooperating locking means disposed on said posterior section and said main support section for adjustably joining said sections for controlled limited anterior-posterior displacement with respect to each other.