Phonological awareness has been claimed to play an important role in the development of language skills, and it is essential that the child's phonological skills be assessed accurately in order to predict and to take early measures to help those that may encounter problems. Although the mora has attracted much attention in the discussion of phonological knowledge and phonological skills of Japanese, to our knowledge there are no previous studies that have assessed disordered speech of Japanese purely from the viewpoint of prosodic levels higher than the mora. In order to fill in this gap, this paper will present data from a child with "unintelligible speech". The longitudinal data (4; 11 to 8;6) collected from spontaneous Japanese speech were analysed from the perspective of phonological markedness. The evidence so far indicates that even within severely distorted speech, it may be possible to tease out systematic errors that seem to suggest the existence of unmarked phonological structures such as the bimoraic foot. This finding suggests that in order to accurately assess a child's phonological ability, many different levels within the phonological hierarchy should be taken into consideration. (Contains 6 figures and 4 tables.)