This study investigated children's acquisition of Hong Kong Cantonese. 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. 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(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 (≥ 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. 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.