We present four children, three of them boys, affected with an identical clinical pattern consisting of early-onset ataxia, delayed dentition, hypomyelination and cerebellar atrophy. Dental radiographs showed variable absence of succedaneous teeth. Proton MR spectroscopy in one child showed elevated white matter myo-inositol. As the clinical and radiological picture in these patients is identical to that of four cases described earlier, we suggest that this disorder with ataxia, delayed dentition and hypomyelination (ADDH) represents a new entity. With the characteristic tooth abnormalities it should be straightforward to identify new patients in order to facilitate the search for the underlying genetic defect.