This study included 92 patients with an accessory navicular (AN) noted on an anteroposterior roentgenography. This group was selected from 860 patients admitted to the authors' gait analysis laboratory. The medial longitudinal arch was evaluated by using an "arch index" calculated from the pressure picture obtained from a pressure distribution measurement system. The average arch index was 0.15 and there was no significant correlation between AN types and arch index. The study concluded that the presence and type of AN are not correlated with the height of the medial longitudinal arch of the foot and that AN is not associated with pes planus.