Purpose: The purpose of this study was to examine the diagnostic accuracy of traditional measures of phonological ability developed for monolingual English-speaking children with their bilingual peers in both English and Spanish. We predicted that a composite measure, derived from a combination of English and Spanish phonological measures, would result in higher diagnostic accuracy than examining the individual phonological measures of bilingual children separately by language. Method: Sixty-six children, ages 3;3-6;3 (years; months), participated in this study: 29 typically developing bilingual Spanish-English-speaking children (x = 5;3), five bilingual Spanish-English-speaking children with speech sound disorders (x = 4;6), 26 typically developing monolingual English-speaking children (x = 4;8), and six monolingual English-speaking children with speech sound disorders (x = 4;9). Children were recorded producing single words using the Assessments of English and Spanish Phonology, and productions were phonetically transcribed and analyzed using the Logical International Phonetics Program. Overall consonants correct-revised; accuracy of early-, middle-, and late-developing sounds; and percent occurrence of phonological error patterns in both English and Spanish were calculated. Receiver operating characteristic curves and support vector machine models were applied to observe diagnostic accuracy, separately and combined, for each speaker group and each language. Results: Findings indicated the combination of measures improved diagnostic accuracy within both the English and Spanish of bilingual children and significantly increased accuracy when measures from both languages of bilingual children were combined. Combining measures for the productions of monolingual English-speaking children did not increase diagnostic accuracy. Conclusion: To prevent misdiagnosis of speech sound disorders in bilingual preschoolers, the composite phonological abilities of bilingual children need to be assessed across both gross and discrete measures of phonological ability.