The colonization of Sitka spruce stumps byHeterobasidion annosum, and the population structure of colonies, was determined 2–3 yrs after inoculation with a 10‐fold dilution series of basidiospore suspensions. Artificially inoculated stumps were infected more frequently than the controls, which received only natural inoculum. The extent of colonization tended to increase with increasing dilution and reached a maximum at the penultimate dilution, but differences were not significant because of large within‐treatment variation. At the higher dilutions stumps fell into poorly‐colonized and heavily‐colonized groups suggesting that some stumps are inhibitory to infection whereas others are extremely susceptible. Colonized areas resulting from the higher dilution treatments tended to comprise fewer larger genets than those from more highly concentrated spore treatments. The results suggest that the success of establishment byH. annosumin basidiospore‐colonized stumps represents the outcome principally of intraspecific competition and the constraints on colonization operating within stumps.