Purpose: This study investigated children's acquisition of Hong Kong Cantonese. Method: Participants were 1,726 children ages 2;4 to 12;4 (years;months). Single-word speech samples were collected to examine 4 measures: initial consonants, final consonants, vowels/diphthongs, and lexical tones. A 2-way analysis of variance was performed to examine the effects of age and sex on phoneme acquisition. Results: There was rapid acquisition of initial consonants from age 2;6 to age 4;6. All 19 initial consonants were acquired by age 6;0 (90% criterion): /p-/, /m-/, and /j-/ were acquired the earliest; the last were /ts [superscript h]-/ and /s-/. Final consonants had a different acquisition time from their initial counterparts. Vowels were acquired by age 5;0 and diphthongs by age 4;0. All 9 tones were acquired by age 2;6. The main effect of age was significant for all 4 measures, whereas sex was significant for all measures except tone. Common phonological patterns (greater than or equal to 10%) for initial consonants were stopping, fronting, deaspiration, delabialization, affrication, and nasalization; patterns with 5.0%-9.9% occurrence were backing, deaffrication, gliding, and dentalization. Conclusions: The acquisition of Cantonese showed similarities with English acquisition yet also had specific characteristics. Factors that contributed to the acquisition rate were functional load, articulatory ease, consonant-vowel interactions, phonetic variations, and the behavior of vowels and their allophones.