Leukoencephalopathy with brain stem and spinal cord involvement and elevated white matter lactate (LBSL) is a very rare autosomal recessive mitochondrial disorder. Clinically patients have slowly progressive ataxia, pyramidal syndrome and dorsal column dysfunction. The disease is defined on the basis of characteristic abnormalities observed on magnetic resonance imaging such as inhomogeneous, spotty involvement of the cerebral white matter, selective involvement of brain stem and spinal cord tracts as well as lactate elevation in the affected white matter on spectroscopy. We present the first identified Polish patient suffering from LBSL confirmed molecularly. © 2010 The Japanese Society of Child Neurology.