PURPOSE: To verify the changes in the deviant phonological system regarding phonemes acquisition and in the severity level of phonological disorders in subjects submitted to phonological therapy using the contrastive approach, in comparison to a group of subjects not submitted to intervention. METHODS: Participants were 18 subjects aged between 4 years and 10 months and 7 years and 4 months, of both genders, with diagnosis of phonological disorder. Nine subjects treated by contrastive approach constituted the Experimental Group, and the other nine subjects, the Control Group (on the waiting list for phonological therapy). All subjects were assessed before and after the period of contrastive therapy applied only to the Experimental Group. Subjects in both groups were matched by age, severity level of the phonological disorder, number of absent sounds in the first phonological assessment, and period of time between the first and the second phonological assessment. In both assessments, the number of acquired sounds in the general phonological system was verified and the Percentage of Consonants Correct - Revised was calculated to determine the severity level of the phonological disorder. Data were statistically analyzed. RESULTS: The Experimental Group acquired more sounds, which determined changes in the severity level of the phonological disorder. The differences found between groups were significant. CONCLUSION: The phonological therapy using the contrastive approach promotes changes in the phonological system that significantly influence the acquisition of sounds and the change of the severity level.