1. Roost-dead Grey Starlings, Sturnus cineraceus, were collected through the winter roosting period at three large roosts, Koshigaya in Saitama, Shinhama in Chiba and Kozukue in Kanagawa Prefectures.2. The roosts were used from November to middle March. The dead birds were found from January at Koshigaya and from Feburary at Shinhama and Kozukue.3. Research areas for collection of roost-dead birds were marked, which were 33m2. (total of 3 sections), 116m2. (total of 3 sections) and 466m2. (total of 4 sections) at Koshigaya, Shinhama and Kozukue respectively. But, actual research area for dead-bird collection was much larger at Koshigaya, and these research areas covered 50%, 30% and 90% of entire roosting areas at Koshigaya, Shinhama and Kozukue respectively. In all, the numbers of dead birds collected were 40 at Koshigaya, 10 at Shinhama and 24 at Kozukue, and except only 5 examples, the cause of death was a same kind of disease. Two Dusky Thrushes and one Brown-eared Bulbul, probably of this cause, were found dead.4. The total number of roosting birds were determined by counts of returning birds to the roost which was: 50, 000 birds at Koshigaya, 8, 000 birds at Shinhama and 6, 000 birds (probably underestimated owing to a windy day count) at Kozukue.5. The pathological diagnostic symptoms characteristic to the roost-dead birds were: 1) Cranial hemorrhage of various degrees occurring in the brain and skull (between the bony plate) which often accompanied severe orbital hemorrhage and protrusion of eye-balls caused by 'flooding' of the brain into the orbit. 2) Congestion of various degrees in the lung, which is usually heavier on the right side. 3) Often pathologic enlargement of the heart filled with venous blood. 4) Often hemorrhage of jugular vein or along the spinal cord (after Prof. Miyamoto) and the capillaries of various body parts. The gizzard was always, except a single case, empty. The pectoral muscles were normal or slightly, or rarely considerably, weakened, and the fat varied in amount by individual from much to none.6. Young Sparganum mansoni (Cestoda) were found in 8 birds out of 69 examples examined, parasitizing subcutaneously on the surface of pectoral muscles or inner side of the thigh muscles; probably the first record in wild birds. It was also found in the intestine in 26% examples examined, and other parasite, Acanthocephala (and one Cestoda sp.) was found in 21% examples. Pathological examination made by Prof. Tabe, as well as Dr. Kametani and Miss Kihara, parasitologists, did not prove the presence of cercaria and eggs of Gigantobilhazia sturniae Tabe (1948) known in this starling from other prefectures. Results of anatomical, histological and some bacteriologic and pesticide examinations done by Prof. Miyamoto are also included, but direct factor causing the fatal cranial and lung diseases has not been clarified.7. Ecologically, it was found that 1) Average 71%, even 80% at Koshigaya, of the roost-dead birds were males, 3) Seasonally, January and February were the peak of the disease. Considerations were given from some ecological point of view.8. The roost-mortality was estimated from two calculations. The roosting density was estimated conservatively as 15 birds in 1m2. (indirect photographic data, though night flash-photos were not available were considered), and based on the collected dead birds within the measured research areas, the mortality was estimated as 1.01% at Koshigaya, 0.46% at Shinhama and 0.24% at Kozukue. The high % of Koshigaya was apparently due to too small measured area. On the other hand, the mortality was calculated also the other way based on the % of estimated total of dead birds, calculated from the collected dead birds and the % of area covered to entire roost area.