Kraepelinian dichotomy between schizophrenia (SCZ) and bipolar disorder (BD) is based on the increased degree of overlap in the pathophysiology of the two disorders and white matter pathology has emerged as a possible marker for these illnesses. Indeed, genes regulating myelin and oligodendrocytes are downregulated in both SCZ and BD, suggesting oligodendrocyte dysfunction. Also, we and others have demonstrated using MRI intra- and inter-cortical white matter impaired connectivity in both disorders. These accumulating data suggests a possible common physiological pathway for SCZ and BD, involving white matter disconnection. White matter microstructure organization can now be explored by diffusion imaging. Recently, we have shown with diffusion MRI impairment of frontal and temporal white matter, corpus callosum, and thalamus in one of the largest population of patients with SCZ reported in the literature. Also, white matter microstructure alterations have also been found in BD, and our diffusion imaging data would confirm that in our population of BD patients. Therefore there is strong evidence suggesting that white matter pathology is present in both SCZ and BD, possibly representing a common intermediate endophenotype. This may potentially be sustained by dysfunctional olygodendrocytes, leading to white matter disruption and ultimately to cognitive disturbances. Impairments of executive functions are indeed reported in both SCZ and BPD and epidemiological studies have demonstrated family aggregation of both disorders. In conclusion, in this symposium we hope to inform on the current debate on the merits of the Kraepelinian dichotomy, characterizing the dimensional approach in the understanding of the functional psychoses.