ABSTRACT Purpose To identify the indicators of speech fluency that differs subjects with stuttering, with phonological disorder, and with the two disorders in comorbidity. Methods Thirty subjects aged 4-11 years old were divided into 3 groups, each one with 10 subjects: groups with developmental stuttering (SG), phonological disorder (PDG), and with two diagnoses in comorbidity (SPDG) participated in this study. The procedures were speech fluency and phonology evaluation. The data were submitted to statistical analysis. Results Subjects from SG and SPDG showed a greater occurrence of stuttering-like disfluencies and total of disfluencies in relation to the subjects with PDG. Regarding to the other disfluencies, the three groups were similar. Subjects with PDG showed fewer monosyllabic word repetitions, part of word repetition and prolongations in relation to subjects from SG and SPDG. Blocks occurred more frequently in the two groups with stuttering (SG and SPDG) than in the group with PDG. Interjection occurred more frequently in subjects from SG than in PDG. Conclusion The PDG was the most differentiated in quantitative and qualitative terms in the three groups analyzed. The similarities and differences between the groups will assist the differential diagnosis and, consequently, will enable improved therapy. The presence of blocks represents an important marker for the diagnosis of stuttering