Ectomycorrhizal (ECM) diversity was measured in 12 mixed-wood stands in the Abitibi region of north-western Québec. Stands were of similar age and were situated on similar mineral soil deposits, but supported varying proportions of ECM host trees. Host roots were sampled in a manner that enabled their separation into species on the basis of wood anatomy. Shannon diversity indices for the ECM colonizing each host species were determined on the basis of ECM anatomy. The diversity of overstory trees, understory plants and host roots, as well as overstory tree composition, root density and pertinent abiotic factors were measured and used as independent variables in multiple regressions against ECM diversity. We found a positive relationship between overstory tree diversity and ECM diversity, which appears related to fungal host specificity. Although no direct relationship was seen between ECM diversity and soil factors, levels of exchangeable base cations were related to ECM fungal species composition which correlated with ECM diversity at the scale sampled.