This article presents a new comprehensive assessment of the Holocene hydrological variability of Lake Ladoga, northwest Russia. The reconstruction is based on oxygen isotopes of lacustrine diatom silica (O-18(diatom)) preserved in sediment core Co 1309, and is complemented by a diatom assemblage analysis and a survey of modern isotope hydrology. The data indicate that Lake Ladoga has existed as a freshwater reservoir since at least 10.8cal. ka BP. The O-18(diatom) values range from +29.8 to +35.0 parts per thousand, and relatively higher O-18(diatom) values around +34.7 parts per thousand between c. 7.1 and 5.7cal. ka BP are considered to reflect the Holocene Thermal Maximum. A continuous depletion in O-18(diatom) since c. 6.1cal. ka BP accelerates after c. 4cal. ka BP, indicating Middle to Late Holocene cooling that culminates during the interval 0.8-0.2cal. ka BP, corresponding to the Little Ice Age. Lake-level rises result in lower O-18(diatom) values, whereas lower lake levels cause higher O-18(diatom) values. The diatom isotope record gives an indication for a rather early opening of the Neva River outflow at c. 4.4-4.0cal. ka BP. Generally, overall high O-18(diatom) values around +33.5 parts per thousand characterize a persistent evaporative lake system throughout the Holocene. As the Lake Ladoga O-18(diatom) record is roughly in line with the 60 degrees N summer insolation, a linkage to broader-scale climate change is likely.