Marked lateral ventricular enlargement associated with atrophic cerebral cortex is described in three dogs. In case 1 (Irish terrier) and case 2 (German shepherd), hydranencephaly was diagnosed and it was characterized by the complete loss of cerebral hemispheres, leaving only about 2 mm of brain tissue that encircled fluid filled sacs. Clinically, the Irish terrier showed only sleepines and retroflexion of the head during sleeping, while the German shepherd showed no neurological or any other symptoms. In the third case (English setter), internal hydrocephalus was found, probably secondary to the severe periventricular lesions characterized by neutrophilic/ mononuclear cell infiltration. This lesion was diagnosed as hydrocephalus associated with periventricular encephalitis, and this dog showed more severe neurological symptoms, such as: somnolence, opisthotonus, rigor of muscles due to seizures, poor eye-sight, stager, ataxia, and unresponsivness to vocalisation. In all cases, no infectious agent or specific cause was determined. Key words: dog, cavitatory lesions, hydranencephaly, hydrocephalus, periven_ricular encephalitis Vrlo jako prosirenje lateralnih mozdanih klijetki praceno s jakom atrofijom mozdane kore prikazano je kod tri psa. U prvom slucaju (irski terijer) i drugom slucaju (njemacki ovcar) opisana je hidranencefalija karakterizirana potpunim gubitkom mozdanih polutki ostavljajuci samo oko 2 mm mozdanog tkiva sto predstavlja tekucinom ispunjene vrece. Klinicki je irski terijer pokazivao samo pospanost i retrofleksiju glave tijekom spavanja, a njemacki ovcar nije pokazivao neuroloske ni druge znakove bolesti. U trecem slucaju (engleski seter), unutarnji hidrocefalus vjerojatno je bio sekundaran zbog teskog periventrikularnog ostecenja karakteriziranog neutrofilnim/mononuklearnim stanicnim infiltratom. Ta je lezija dijagnosticirana kao hidrocefalus povezan s periventrikularnim encefalitisom, a pas je pokazivao teske neuroloske znakove kao sto su pospanost, opistotonus, grcevi misica, poteskoce s vidom, vrtoglavica, ataksija i nereagiranje na zvucne podrazaje. U sva tri slucaja nije utvrden infekciozni ni drugi specifican uzrok. Kljucne rijeci: pas, kavitatorne lezije, hidranencefalija, hidrocefalus, perivaskularni encefalitis