The article briefly relates the history of the botanical reserve of curly (or Karelian) birch Betula pendula Roth var. carelica (Mercklin) Hämet-Ahti Anisimovshchina (granted its official status in 1984) and describes its key parameters. The nature reserve was founded on the basis of the largest natural population of these trees in Karelia, located in the south-east of the republic (northern part of Zaonezhsky Peninsula), which had long been known among locals but with no targeted conservation efforts until the early 20th century. The last century of its actual functioning history roughly falls into three periods: 1) Soviet, pre-WWII; 2) Soviet, post-WWII, and 3) post-Soviet. Due to its low numbers, the protection status of curly birch was recognized since the very start of studies (early 1930s). Even so, and despite certain actions supported by relevant decisions of regional executive authorities, not only the size of this unique natural population, where curly birch was the dominant species, but also the area it occupied declined over time. The factors listed as the main causes of the ongoing changes are: low competitive capacity, critical age of trees, near absence of viable advance regeneration, irregular tending, illegal harvesting, etc. The main negative consequences of these changes apparently include a decline in the population’s genetic diversity and the trend for its regression (age structure deterioration). The article reports that by the end of the 20th century there were over 3200 curly birch trees growing in Anisimovshchina BR and describes some of their phenotypic traits. By the beginning of the 21st century, this population had declined markedly for various reasons. However although there is no accurate data on the number of curly birch trees in Anisimovshchina BR to date, its natural population can still be regarded as the largest and the only in Karelia as well as in Russia as a whole, and so demands special attention.