This study applies the Phonological Mean Length of Utterance measurement (PMLU; Ingram & Ingram, 2001; Ingram, 2002) to the data of five children acquiring Finnish and evaluates their phonological development longitudinally at four different age points: 2;0, 2;6, 3;0, and 3;6. The children's results on PMLU and related measures are discussed together with remarks on individual differences regarding the acquisition of consonants, consonant clusters and word length. During the period analyzed the children's phonetic inventories increase and they gradually overcome the constraints against long words and consonant sequences. The PMLU method's ability to reflect the qualitative changes and individual differences between the children is found to be limited in some respects, although overall development can be noted in the values. The PMLU method's strengths and weaknesses are evaluated critically and improvements suggested. (Contains 6 tables and 4 footnotes.)