SUMMARY Relations between above‐ground fruitbodies of mycorrhizal fungi and mycorrhizas in the soil were studied in 23 Douglas fir stands of various ages in The Netherlands. In the autumn of 1986, fruitbody and mycorrhiza density and diversity were determined. Quantitative relations were found between above‐ground fruitbodies of mycorrhizal fungi and below‐ground mycorrhizas. Mycorrhiza density explains fruitbody density better than mycorrhiza frequency, but fruitbody density is an unreliable estimator of mycorrhiza density. Density of root tips does not influence the density of fruitbodies. The above‐ground diversity, in number of species of fruitbodies, is reflected by the below‐ground diversity, in number of mycorrhiza types, but the below‐ground diversity is not explained simply by the number of species fruiting. The strong decline in density and diversity of fruitbodies and mycorrhizas with age of the stands cannot be explained yet.