Speech sound disorders take a large part in a practical work of a speech-language pathologists around the world as well as in Croatia. Although speech sound disorders were traditionally discussed in the context of articulation disorders, with the advancements of lingvistics it is increasingly talked about them as phonological disorders. Defining phonological disorder is hardened because of the terminological overlapping with articulation disorder, as well as their frequent comorbidity. Since differential diagnosis is of utmost importance in order to meet the highest standard of clinical practice in service delivery, with not having many papers about the subject in Croatia, a research was conducted amongst 75 Croatian speech-language pathologists via an on-line questionnaire to determine their knowledge of differential-diagnostics criteria in diagnosis of articulation and phonological disorders. In addition to knowing the diagnostic criteria, the ways in which phonological disorders are assessed were examined in order to gain insights from practice and identify possible problems that speech-language pathologists encounter. The sample was divided in two groups, the older generation respondents who graduated before 2011, and the younger generation respondents who graduated after 2011 (2011 included). This year was taken as a criterion since students of the 2011 graduating generation were the first generation of students to take a Phonological Disorders course as part of their study at the Faculty of Education and Rehabilitation Sciences in Zagreb. Carrying out the research with the t-test revealed a statistically significant difference between the groups, that is, younger generations of speech-language pathologists are more familiar with the differential-diagnostic criteria of articulation and phonological disorders. Further results indicate that knowledge of the differential-diagnostic criteria is not affected by which source the respondents received information about phonological disorders or how many cases of phonological disorders they encounter per year. Qualitative analysis of the answers revealed that Croatian speech-language pathologists mostly include the assessment of oral motor skills and connected speech sample in the assessment of phonological disorders, taking into account the auditory status, often using non-standardized assessment methods, with the most frequent procedures being repeating nonsense syllables, nonwords and real words. Phonological processes are recorded by 51% of the respondents, and qualitative analysis of the responses revealed deficiencies in the systematic naming and recognition of phonological processes, although Croatian speech-language pathologists are well aware of the main features of phonological disorder. The data from this research indicate the need for a more detailed study of the problem of the profession, as well as the creation of guidelines for work at the national level.