Hydrocephalus associated lesions such as diverticula, clefts and tears observed in periventricular white matter were studied pathologically in three puppies with necropsy between 1993 and 1994. Enlargement of the cranial vault was present in the puppies. The animals were blind, and their morphological alterations were similar. Marked hydrocephalus caused by mesencephalic canal malformations and obstruction was detected in all cases. Compression atrophy was seen in the nucleus caudatus, hippocampus, putamen and cerebellum in all animals. Cerebral sulci malformations were also detected in the cranial parts of the brain. Ependymal lesions consisting of attenuation, regeneration, calcification and desquamation were also observed. Bilateral periventricular diverticula and cleft formation were found in the area of the nucleus caudatus. Tears were seen within the residual hemispheric tissue and at the border of the internal capsule and putamen. Perivascular fibrous tissue formation, neovascularisation, haemorrhage and diffuse gliosis were other findings caused by the pressure of cerebrospinal fluids (CSF). Hence, we considered that all changes observed in the periventricular white matter of the puppies in this study were caused by CSF.