background: the therapeutic evolution of two subjects with different degree of phonological disorder treated by empty set with minimal distinction of distinctive traces. procedures: the sample was made up by two male subjects with phonological disorder. s1, age 4:5-year old, with mild-moderate phonological disorder, and s2, age 6:4-year old, with moderate-severe phonological disorder. both were treated by empty set with minimal distinction of traces. after treatment, we compared the initial and final phonological evaluation. results: s1 acquired in less time the selected target sounds, however, both subjects showed generalizations to untreated words and to other word positions. only s2 showed generalization across and within other sound classes. conclusion: the empty set with minimal distinction of distinctive traces was effective for the treatment of mild-moderate and moderate-severe disorders because both subjects showed improvement as for the speech.