There has been little or no research on Vietnamese phonological development, let alone on phonological disorders of Vietnamese-speaking children. The goal of this study is to evaluate the sound systems of monolingual Vietnamese-speaking children with phonological impairment. Independent and relational analyses of four children (ages 4;4 to 5;5) are presented in terms of error patterns, dialectal patterns, phonotactic constraints, and phonetic and phonemic inventories. The characteristics of these children's sound systems are compared to studies of phonological acquisition of other languages, in order to identify characteristics that may be universal versus those that may be language-specific in nature. (Contains 6 tables.)