This paper reports the results of a study of the persistence of individual differences in the phonological development of 10 normally developing children observed at age 1 year and again at age 3 years. Data were based on 1/2-hr audio and video recordings of weekly spontaneous mother-child interaction sessions in the home between 9 and 17 months and at 36 months. In addition, phonological and cognitive probes were administered at age 3. At age 1 the children were compared at four times selected on the basis of the number of different word types used in a session. Preferences for particular phonological categories (fricatives, liquids, final consonants) were found not to correspond to relative mastery of those categories at age 3. Based on both babble and words, high use of vocalizations containing true consonants was found to be predictive of greater phonological advance at age 3. Phonological errors of two kinds were distinguished for age 3: those resulting from difficulty with specific segments and those more typical of younger children, involving the rearrangement, assimilation, or deletion of segments or syllables (prosodic errors). The children differed in intelligibility and in specific segment substitutions and cluster reductions. They also differed in the proportion of prosodic errors made and in consistency in segmental errors. Lastly, aspects of cognitive or learning style as expressed in phonological organization were found to be recognizable at both age 1 and age 3.