Five mixed populations of Dryopteris dilatata and D. filix-mas have been studied in deciduous woods near Derby, England. It has been shown that in selected populations of each species, the plants were significantly clumped. It has also been shown that small plants of each species in all populations tended to grow amongst bryophytes, whilst larger ones grew in a wider range of habitats. All populations of D. dilatata showed an excess of small, sterile plants over larger, fertile ones. All but one of the D. filix-mas populations showed an excess of large, fertile plants over small, sterile ones, while the remaining one showed roughly equal numbers of large, fertile plants and small sterile ones. The population dynamics of two populations of each species have been studied so far over two seasons. This has shown that plants may increase or decrease in size or remain the same size between years. Mortality has been shown to be very size-specific in that smaller plants have a much lower chance of survival. Colonisation by new plants was mostly in bryophytes near established plants. The significance of these observations for the population dynamics of the species is discussed.