LIM-homeodomain genes encode a family of transcription factors with highly conserved roles in the patterning and regionalisation of the vertebrate brain. The expression of one of those genes, Lhx15, in the embryonic lamprey brain, characterises precise functional subdivisions. In order to analyse the non-embryonic development of the lamprey brain, we chose this gene to perform in situ hybridisations in Petromyzon marinus larvae of different ages. We demonstrate the usefulness of Lhx15 to follow the development and morphogenesis of brain structures and show the dynamical expression of this gene through time. Furthermore, we provide evidence for the evolutionary conservation of the expression of this gene in the spinal cord, notochord and urogenital system.