The reproductive behaviour in a high-density situation of the sp. was investigated in northern Poland in 1993 and 1995. Because of their high density, males were non-territorial. After a very brief tandem flight, copulations took place either on the ground or in the surrounding pine trees and lasted, on average, 640 s. Afterwards the male guarded the female while she was on post-copulatory rest (PCR). During PCR (which occurred in 11 out of 13 observed cases), the male bent his abdomen tip up to the basal segments after a mean time of 81 s. This behaviour was interpreted as intra-male sperm translocation (ST). Oviposition took place over open water. During mating time, from 10:00 h to about 17:00 CEST, almost none of the observed ovipositions was completed undisturbed. Outside this time, half of the ovipositions observed was completed undisturbed. The latter lasted 34 s, in which the female had an average frequency of 0.6 to 1.9 dips per s. Eleven hand-held ovipositions revealed a mean egg number of 327 eggs per female and a mean egg flow rate of 4,6 eggs s '. It is concluded that the mating system of L. albifrons is best described as a combination of resource limitation and female control. Some known effects of high male density on the reproductive behaviour of the Libellulidae are discussed.