Flowering plants of some populations of Orchis mascula (L.) L. occurring in the most southern part of the Dutch province of Limburg were studied during the period 1960—70. From each flowering plant the following data were recorded: total height of the plant and length of inflorescence. The sites are situated in formerly coppice woodland on differently facing slopes at a varying altitude above sea level. The woodland belongs to the Stellario — Carpinetum subass. orchidetosum. The number of flowering plants fluctuated from year to year on each locality. Also the height of the total plant and the length of the inflorescence are very variable. A correlation between increasing number of flowering plants and increasing total height of plants could not be established. The height of the total plant and the length of inflorescence are strongly correlated with each other. The length of the inflorescence can be seen as a standard for the number of flowers per inflorescence. Some ecological aspects concerning the variation in the number of flowering plants in a population from year to year are discussed in detail.