This work was based on the Skinnerian model of selection by consequences and on the biobehavioralmodel of activity anorexia, in order to interpret the so called anorexia andbulimia nervosa, emphasizing the multiple determination of such eating disorder. Thepresent study aimed at investigating the variables involved in the origin and maintenance ofthe eating disorders of four participants treated at an outpatient program for eatingdisorders of a university hospital (PROATA ? UNIFESP). The relationships betweenphysical activity and eating restrictions (dieting), which are considered a risk for anorexia,as well as the acting contingencies probably involved on the maintenance of the eatingdisorders were investigated. The results indicated a probable relationship betweenexercising and feeding restrictions at the origin of the patients referred eating disorders, andallowed for the identification of the acting contingencies involved in their maintenance