Nonuniformity of elementary filaments in the spinning of polyacrylonitrile yarns has been studied. It has been shown that the spinning conditions (spinneret hole diameter, concentration and temperature of the precipitation bath) have only a slight effect on the nonuniformity of elementary filaments. Nonuniformity rises along the course of the technological process. The suggestion has been made that the increase in nonuniformity of elementary filaments with respect to diameter is connected with structural nonuniformity in the freshly spun fibres and with the presence of gel particles in the spinning solutions, which lead to an increase in nonuniformity during stretching.